Modularize webui_util.h

Several desktop-only methods are moved to webui_util_desktop. These
methods are marked as deprecated, as they use disallowed methods.

Bug: 339497734
Change-Id: I5f58ab882b8325581ec66290f69c98131fb3b6af
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5528814
Commit-Queue: Erik Chen <erikchen@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1299545}

chrome/browser/ash/system_web_apps/test_support/BUILD.gn

@@ -33,6 +33,7 @@ source_set("test_support") {
     "//chrome/browser/ash/system_web_apps/types",
     "//chrome/browser/profiles:profile",
     "//chrome/browser/ui",
+    "//chrome/browser/ui/webui",
     "//chrome/browser/web_applications",
     "//chrome/browser/web_applications:web_applications_test_support",
     "//components/crx_file",

chrome/browser/ui/BUILD.gn

@@ -376,8 +376,6 @@ static_library("ui") {
     "webui/version/version_ui.h",
     "webui/webui_load_timer.cc",
     "webui/webui_load_timer.h",
-    "webui/webui_util.cc",
-    "webui/webui_util.h",
     "zoom/chrome_zoom_level_otr_delegate.cc",
     "zoom/chrome_zoom_level_otr_delegate.h",
     "zoom/chrome_zoom_level_prefs.cc",
@@ -469,6 +467,7 @@ static_library("ui") {
     "//chrome/browser/storage_access_api",
     "//chrome/browser/themes",
     "//chrome/browser/ui/side_panel:side_panel_enums",
+    "//chrome/browser/ui/webui",
     "//chrome/browser/ui/webui/data_sharing_internals:mojo_bindings",
     "//chrome/browser/ui/webui/location_internals:mojo_bindings",
     "//chrome/browser/ui/webui/omnibox:mojo_bindings",
@@ -2045,6 +2044,8 @@ static_library("ui") {
       "webui/web_app_internals/web_app_internals_ui.h",
       "webui/webui_gallery/webui_gallery_ui.cc",
       "webui/webui_gallery/webui_gallery_ui.h",
+      "webui/webui_util_desktop.cc",
+      "webui/webui_util_desktop.h",
       "webui/whats_new/whats_new_handler.cc",
       "webui/whats_new/whats_new_handler.h",
       "webui/whats_new/whats_new_ui.cc",

chrome/browser/ui/webui/BUILD.gn

@@ -65,3 +65,21 @@ source_set("configs") {
     }
   }
 }
+
+source_set("webui") {
+  sources = [
+    "webui_util.cc",
+    "webui_util.h",
+  ]
+  deps = [
+    "//base",
+    "//content/public/browser",
+    "//content/public/common",
+    "//services/network/public/mojom",
+    "//ui/base",
+    "//ui/resources",
+  ]
+  if (is_chromeos_lacros) {
+    deps += [ "//chromeos/startup" ]
+  }
+}

chrome/browser/ui/webui/favicon_source.cc

@@ -16,7 +16,7 @@
 #include "chrome/browser/history/top_sites_factory.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/search/instant_service.h"
-#include "chrome/browser/ui/webui/webui_util.h"
+#include "chrome/browser/ui/webui/webui_util_desktop.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/common/webui_url_constants.h"
 #include "components/favicon/core/history_ui_favicon_request_handler.h"
@@ -218,7 +218,7 @@ bool FaviconSource::ShouldServiceRequest(
 
 ui::NativeTheme* FaviconSource::GetNativeTheme(
     const content::WebContents::Getter& wc_getter) {
-  return webui::GetNativeTheme(wc_getter.Run());
+  return webui::GetNativeThemeDeprecated(wc_getter.Run());
 }
 
 void FaviconSource::OnFaviconDataAvailable(

chrome/browser/ui/webui/new_tab_page/new_tab_page_handler.cc

@@ -54,7 +54,7 @@
 #include "chrome/browser/ui/side_panel/customize_chrome/customize_chrome_utils.h"
 #include "chrome/browser/ui/webui/new_tab_page/ntp_pref_names.h"
 #include "chrome/browser/ui/webui/side_panel/customize_chrome/customize_chrome_section.h"
-#include "chrome/browser/ui/webui/webui_util.h"
+#include "chrome/browser/ui/webui/webui_util_desktop.h"
 #include "chrome/common/chrome_features.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/url_constants.h"
@@ -474,7 +474,7 @@ NewTabPageHandler::NewTabPageHandler(
           NtpBackgroundServiceFactory::GetForProfile(profile)),
       ntp_custom_background_service_(ntp_custom_background_service),
       logo_service_(logo_service),
-      theme_provider_(webui::GetThemeProvider(web_contents)),
+      theme_provider_(webui::GetThemeProviderDeprecated(web_contents)),
       theme_service_(theme_service),
       profile_(profile),
       web_contents_(web_contents),

chrome/browser/ui/webui/new_tab_page/new_tab_page_handler_unittest.cc

@@ -40,7 +40,7 @@
 #include "chrome/browser/ui/side_panel/customize_chrome/customize_chrome_tab_helper.h"
 #include "chrome/browser/ui/webui/new_tab_page/new_tab_page.mojom.h"
 #include "chrome/browser/ui/webui/side_panel/customize_chrome/customize_chrome_section.h"
-#include "chrome/browser/ui/webui/webui_util.h"
+#include "chrome/browser/ui/webui/webui_util_desktop.h"
 #include "chrome/common/chrome_features.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/webui_url_constants.h"
@@ -319,7 +319,7 @@ class NewTabPageHandlerTest : public testing::Test {
                   VerifyCustomBackgroundImageURL)
           .Times(1);
     }
-    webui::SetThemeProviderForTesting(&mock_theme_provider_);
+    webui::SetThemeProviderForTestingDeprecated(&mock_theme_provider_);
     web_contents_->SetColorProviderSource(&mock_color_provider_source_);
 
     EXPECT_FALSE(

chrome/browser/ui/webui/new_tab_page_third_party/new_tab_page_third_party_handler.cc

@@ -11,7 +11,7 @@
 #include "chrome/browser/themes/theme_service_factory.h"
 #include "chrome/browser/ui/color/chrome_color_id.h"
 #include "chrome/browser/ui/webui/ntp/ntp_resource_cache.h"
-#include "chrome/browser/ui/webui/webui_util.h"
+#include "chrome/browser/ui/webui/webui_util_desktop.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/grit/theme_resources.h"
 #include "components/prefs/pref_service.h"
@@ -55,7 +55,7 @@ void NewTabPageThirdPartyHandler::NotifyAboutTheme() {
   auto theme = new_tab_page_third_party::mojom::Theme::New();
   auto most_visited = most_visited::mojom::MostVisitedTheme::New();
   const ui::ThemeProvider* theme_provider =
-      webui::GetThemeProvider(web_contents_);
+      webui::GetThemeProviderDeprecated(web_contents_);
   DCHECK(theme_provider);
   const ui::ColorProvider& color_provider = web_contents_->GetColorProvider();
   most_visited->background_color =
@@ -65,8 +65,8 @@ void NewTabPageThirdPartyHandler::NotifyAboutTheme() {
   theme->text_color = color_provider.GetColor(kColorNewTabPageText);
   most_visited->is_dark = !color_utils::IsDark(theme->text_color);
   theme->color_background = color_utils::SkColorToRgbaString(GetThemeColor(
-      webui::GetNativeTheme(web_contents_), web_contents_->GetColorProvider(),
-      kColorNewTabPageBackground));
+      webui::GetNativeThemeDeprecated(web_contents_),
+      web_contents_->GetColorProvider(), kColorNewTabPageBackground));
   if (theme_provider->HasCustomImage(IDR_THEME_NTP_BACKGROUND)) {
     theme->background_tiling = GetNewTabBackgroundTilingCSS(*theme_provider);
     theme->background_position =

chrome/browser/ui/webui/new_tab_page_third_party/new_tab_page_third_party_ui.cc

@@ -19,6 +19,7 @@
 #include "chrome/browser/ui/webui/ntp/ntp_resource_cache.h"
 #include "chrome/browser/ui/webui/theme_source.h"
 #include "chrome/browser/ui/webui/webui_util.h"
+#include "chrome/browser/ui/webui/webui_util_desktop.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/common/webui_url_constants.h"
@@ -63,7 +64,7 @@ void CreateAndAddNewTabPageThirdPartyUiHtmlSource(Profile* profile,
   source->AddLocalizedStrings(kStrings);
 
   const ui::ThemeProvider* theme_provider =
-      webui::GetThemeProvider(web_contents);
+      webui::GetThemeProviderDeprecated(web_contents);
   // TODO(crbug.com/40823895): Always mock theme provider in tests so that
   // `theme_provider` is never nullptr.
   if (theme_provider) {
@@ -74,8 +75,8 @@ void CreateAndAddNewTabPageThirdPartyUiHtmlSource(Profile* profile,
                       GetNewTabBackgroundTilingCSS(*theme_provider));
     source->AddString("colorBackground",
                       color_utils::SkColorToRgbaString(GetThemeColor(
-                          webui::GetNativeTheme(web_contents), color_provider,
-                          kColorNewTabPageBackground)));
+                          webui::GetNativeThemeDeprecated(web_contents),
+                          color_provider, kColorNewTabPageBackground)));
     // TODO(crbug.com/40120448): don't get theme id from profile.
     source->AddString("themeId",
                       profile->GetPrefs()->GetString(prefs::kCurrentThemeID));

chrome/browser/ui/webui/ntp/ntp_resource_cache.cc

@@ -29,7 +29,7 @@
 #include "chrome/browser/ui/cookie_controls/cookie_controls_service_factory.h"
 #include "chrome/browser/ui/layout_constants.h"
 #include "chrome/browser/ui/webui/ntp/cookie_controls_handler.h"
-#include "chrome/browser/ui/webui/webui_util.h"
+#include "chrome/browser/ui/webui/webui_util_desktop.h"
 #include "chrome/common/buildflags.h"
 #include "chrome/common/chrome_features.h"
 #include "chrome/common/pref_names.h"
@@ -401,7 +401,8 @@ void NTPResourceCache::CreateNewTabGuestHTML() {
 void NTPResourceCache::CreateNewTabIncognitoCSS(
     const content::WebContents::Getter& wc_getter) {
   auto* web_contents = wc_getter.Run();
-  const ui::NativeTheme* native_theme = webui::GetNativeTheme(web_contents);
+  const ui::NativeTheme* native_theme =
+      webui::GetNativeThemeDeprecated(web_contents);
   DCHECK(native_theme);
 
   const ui::ThemeProvider& tp = ThemeService::GetThemeProviderForProfile(
@@ -434,7 +435,8 @@ void NTPResourceCache::CreateNewTabIncognitoCSS(
 void NTPResourceCache::CreateNewTabCSS(
     const content::WebContents::Getter& wc_getter) {
   auto* web_contents = wc_getter.Run();
-  const ui::NativeTheme* native_theme = webui::GetNativeTheme(web_contents);
+  const ui::NativeTheme* native_theme =
+      webui::GetNativeThemeDeprecated(web_contents);
   DCHECK(native_theme);
 
   const ui::ThemeProvider& tp =

chrome/browser/ui/webui/tab_strip/tab_strip_page_handler.cc

@@ -39,7 +39,7 @@
 #include "chrome/browser/ui/webui/tab_strip/tab_strip_ui_util.h"
 #include "chrome/browser/ui/webui/theme_source.h"
 #include "chrome/browser/ui/webui/util/image_util.h"
-#include "chrome/browser/ui/webui/webui_util.h"
+#include "chrome/browser/ui/webui/webui_util_desktop.h"
 #include "chrome/grit/generated_resources.h"
 #include "components/tab_groups/tab_group_color.h"
 #include "components/tab_groups/tab_group_id.h"
@@ -191,7 +191,8 @@ TabStripPageHandler::TabStripPageHandler(
   ThemeServiceFactory::GetForProfile(browser_->profile())->AddObserver(this);
 
   // Or native theme change.
-  theme_observation_.Observe(webui::GetNativeTheme(web_ui_->GetWebContents()));
+  theme_observation_.Observe(
+      webui::GetNativeThemeDeprecated(web_ui_->GetWebContents()));
 }
 
 void TabStripPageHandler::NotifyLayoutChanged() {
@@ -886,7 +887,7 @@ void TabStripPageHandler::OnNativeThemeUpdated(
   // switch between light/dark mode. b) A different theme is enabled. e.g.
   // switch between GTK and classic theme on Linux. Reset observer in case b).
   ui::NativeTheme* current_theme =
-      webui::GetNativeTheme(web_ui_->GetWebContents());
+      webui::GetNativeThemeDeprecated(web_ui_->GetWebContents());
   if (observed_theme != current_theme) {
     theme_observation_.Reset();
     theme_observation_.Observe(current_theme);

chrome/browser/ui/webui/tab_strip/tab_strip_page_handler_unittest.cc

@@ -15,7 +15,7 @@
 #include "chrome/browser/ui/webui/tab_strip/tab_strip_ui.h"
 #include "chrome/browser/ui/webui/tab_strip/tab_strip_ui_embedder.h"
 #include "chrome/browser/ui/webui/tab_strip/tab_strip_ui_layout.h"
-#include "chrome/browser/ui/webui/webui_util.h"
+#include "chrome/browser/ui/webui/webui_util_desktop.h"
 #include "chrome/test/base/browser_with_test_window_test.h"
 #include "chrome/test/base/testing_profile_manager.h"
 #include "components/tab_groups/tab_group_color.h"
@@ -702,7 +702,7 @@ TEST_F(TabStripPageHandlerTest, PreventsInvalidGroupDrags) {
 }
 
 TEST_F(TabStripPageHandlerTest, OnThemeChanged) {
-  webui::GetNativeTheme(web_ui()->GetWebContents())
+  webui::GetNativeThemeDeprecated(web_ui()->GetWebContents())
       ->NotifyOnNativeThemeUpdated();
   EXPECT_CALL(page_, ThemeChanged());
 }

chrome/browser/ui/webui/theme_handler.cc

@@ -12,7 +12,7 @@
 #include "chrome/browser/themes/theme_service.h"
 #include "chrome/browser/themes/theme_service_factory.h"
 #include "chrome/browser/ui/webui/theme_source.h"
-#include "chrome/browser/ui/webui/webui_util.h"
+#include "chrome/browser/ui/webui/webui_util_desktop.h"
 #include "chrome/grit/theme_resources.h"
 #include "content/public/browser/web_ui.h"
 
@@ -43,7 +43,7 @@ void ThemeHandler::OnJavascriptAllowed() {
   // Or native theme change.
   if (web_ui()) {
     theme_observation_.Observe(
-        webui::GetNativeTheme(web_ui()->GetWebContents()));
+        webui::GetNativeThemeDeprecated(web_ui()->GetWebContents()));
   }
 }
 
@@ -61,7 +61,7 @@ void ThemeHandler::OnNativeThemeUpdated(ui::NativeTheme* observed_theme) {
   // switch between light/dark mode. b) A different theme is enabled. e.g.
   // switch between GTK and classic theme on Linux. Reset observer in case b).
   ui::NativeTheme* current_theme =
-      webui::GetNativeTheme(web_ui()->GetWebContents());
+      webui::GetNativeThemeDeprecated(web_ui()->GetWebContents());
   if (observed_theme != current_theme) {
     theme_observation_.Reset();
     theme_observation_.Observe(current_theme);

chrome/browser/ui/webui/theme_source_unittest.cc

@@ -2,7 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "chrome/browser/ui/webui/theme_source.h"
+
 #include <stddef.h>
+
 #include <vector>
 
 #include "base/functional/bind.h"
@@ -11,8 +14,7 @@
 #include "base/strings/strcat.h"
 #include "base/test/bind.h"
 #include "chrome/browser/profiles/profile.h"
-#include "chrome/browser/ui/webui/theme_source.h"
-#include "chrome/browser/ui/webui/webui_util.h"
+#include "chrome/browser/ui/webui/webui_util_desktop.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/grit/theme_resources.h"
 #include "chrome/test/base/test_theme_provider.h"
@@ -43,7 +45,7 @@ class WebUISourcesTest : public testing::Test {
 
  private:
   void SetUp() override {
-    webui::SetThemeProviderForTesting(&test_theme_provider_);
+    webui::SetThemeProviderForTestingDeprecated(&test_theme_provider_);
     profile_ = std::make_unique<TestingProfile>();
     theme_source_ = std::make_unique<ThemeSource>(profile_.get());
     test_web_contents_ = content::WebContentsTester::CreateTestWebContents(
@@ -57,7 +59,7 @@ class WebUISourcesTest : public testing::Test {
     test_web_contents_.reset();
     test_web_contents_getter_ = content::WebContents::Getter();
     profile_.reset();
-    webui::SetThemeProviderForTesting(nullptr);
+    webui::SetThemeProviderForTestingDeprecated(nullptr);
   }
 
   void SendResponse(scoped_refptr<base::RefCountedMemory> data) {

chrome/browser/ui/webui/webui_util.cc

@@ -18,26 +18,12 @@
 #include "ui/base/webui/web_ui_util.h"
 #include "ui/resources/grit/webui_resources.h"
 
-#if BUILDFLAG(IS_CHROMEOS_ASH)
-#include "chrome/browser/ash/policy/core/browser_policy_connector_ash.h"
-#include "chrome/browser/browser_process.h"
-#include "chrome/browser/browser_process_platform_part.h"
-#elif BUILDFLAG(IS_WIN) || BUILDFLAG(IS_MAC)
+#if BUILDFLAG(IS_WIN) || BUILDFLAG(IS_MAC)
 #include "base/enterprise_util.h"
 #elif BUILDFLAG(IS_CHROMEOS_LACROS)
 #include "chromeos/startup/browser_params_proxy.h"
 #endif
 
-#if defined(TOOLKIT_VIEWS)
-#include "chrome/browser/profiles/profile.h"
-#include "chrome/browser/ui/browser.h"
-#include "chrome/browser/ui/browser_finder.h"
-#include "chrome/browser/ui/browser_list.h"
-#include "chrome/browser/ui/browser_window.h"
-#include "ui/native_theme/native_theme.h"
-#include "ui/views/widget/widget.h"
-#endif  // defined(TOOLKIT_VIEWS)
-
 namespace webui {
 
 void SetJSModuleDefaults(content::WebUIDataSource* source) {
@@ -134,80 +120,5 @@ void AddLocalizedString(content::WebUIDataSource* source,
   std::erase(str, '&');
   source->AddString(message, str);
 }
-#if defined(TOOLKIT_VIEWS)
-
-namespace {
-const ui::ThemeProvider* g_theme_provider_for_testing = nullptr;
-}  // namespace
-
-ui::NativeTheme* GetNativeTheme(content::WebContents* web_contents) {
-  ui::NativeTheme* native_theme = nullptr;
-
-  if (web_contents) {
-    Browser* browser = chrome::FindBrowserWithTab(web_contents);
-
-    if (browser) {
-      // Find for WebContents hosted in a tab.
-      native_theme = browser->window()->GetNativeTheme();
-    }
-
-    if (!native_theme) {
-      // Find for WebContents hosted in a widget, but not directly in a
-      // Browser. e.g. Tab Search, Read Later.
-      views::Widget* widget = views::Widget::GetTopLevelWidgetForNativeView(
-          web_contents->GetContentNativeView());
-      if (widget)
-        native_theme = widget->GetNativeTheme();
-    }
-  }
-
-  if (!native_theme) {
-    // Find for isolated WebContents, e.g. in tests.
-    // Or when |web_contents| is nullptr, because the renderer is not ready.
-    // TODO(crbug.com/40677117): Remove global accessor to NativeTheme.
-    native_theme = ui::NativeTheme::GetInstanceForNativeUi();
-  }
-
-  return native_theme;
-}
-
-const ui::ThemeProvider* GetThemeProvider(content::WebContents* web_contents) {
-  if (g_theme_provider_for_testing)
-    return g_theme_provider_for_testing;
-
-  auto* browser_window =
-      BrowserWindow::FindBrowserWindowWithWebContents(web_contents);
-
-  if (browser_window)
-    return browser_window->GetThemeProvider();
-
-  // Fallback 1: get the theme provider from the profile's associated browser.
-  // This is used in newly created tabs, e.g. NewTabPageUI, where theming is
-  // required before the WebContents is attached to a browser window.
-  // TODO(crbug.com/40823135): Remove this fallback by associating the
-  // WebContents during navigation.
-  Profile* profile =
-      Profile::FromBrowserContext(web_contents->GetBrowserContext());
-  const Browser* browser = chrome::FindBrowserWithProfile(profile);
-  if (browser)
-    return browser->window()->GetThemeProvider();
-
-  // Fallback 2: get the theme provider from the last created browser.
-  // This is used in ChromeOS, where under multi-signin a browser window can
-  // be sent to another profile.
-  // TODO(crbug.com/40823135): Remove this fallback by associating the
-  // WebContents during navigation.
-  BrowserList* browser_list = BrowserList::GetInstance();
-  browser = browser_list->empty()
-                ? nullptr
-                : *std::prev(BrowserList::GetInstance()->end());
-  return browser ? browser->window()->GetThemeProvider() : nullptr;
-}
-
-void SetThemeProviderForTesting(const ui::ThemeProvider* theme_provider) {
-  g_theme_provider_for_testing = theme_provider;
-}
-
-#endif  // defined(TOOLKIT_VIEWS)
 
 }  // namespace webui

chrome/browser/ui/webui/webui_util.h

@@ -11,15 +11,9 @@
 #include "ui/base/webui/resource_path.h"
 
 namespace content {
-class WebContents;
 class WebUIDataSource;
 }
 
-namespace ui {
-class NativeTheme;
-class ThemeProvider;
-}
-
 namespace webui {
 
 // Performs common setup steps for a |source| using JS modules: enable i18n
@@ -44,20 +38,6 @@ void EnableTrustedTypesCSP(content::WebUIDataSource* source);
 void AddLocalizedString(content::WebUIDataSource* source,
                         const std::string& message,
                         int id);
-#if defined(TOOLKIT_VIEWS)
-
-// Returns whether WebContents should use dark mode colors depending on the
-// theme.
-ui::NativeTheme* GetNativeTheme(content::WebContents* web_contents);
-
-// Returns the ThemeProvider instance associated with the given web contents.
-const ui::ThemeProvider* GetThemeProvider(content::WebContents* web_contents);
-
-// Sets a global theme provider that will be returned when calling
-// webui::GetThemeProvider(). Used only for testing.
-void SetThemeProviderForTesting(const ui::ThemeProvider* theme_provider);
-
-#endif  // defined(TOOLKIT_VIEWS)
 
 }  // namespace webui
 

chrome/browser/ui/webui/webui_util_desktop.cc

@@ -0,0 +1,95 @@
+// Copyright 2024 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/ui/webui/webui_util_desktop.h"
+
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/ui/browser.h"
+#include "chrome/browser/ui/browser_finder.h"
+#include "chrome/browser/ui/browser_list.h"
+#include "chrome/browser/ui/browser_window.h"
+#include "ui/native_theme/native_theme.h"
+#include "ui/views/widget/widget.h"
+
+namespace webui {
+
+namespace {
+const ui::ThemeProvider* g_theme_provider_for_testing = nullptr;
+}  // namespace
+
+ui::NativeTheme* GetNativeThemeDeprecated(content::WebContents* web_contents) {
+  ui::NativeTheme* native_theme = nullptr;
+
+  if (web_contents) {
+    Browser* browser = chrome::FindBrowserWithTab(web_contents);
+
+    if (browser) {
+      // Find for WebContents hosted in a tab.
+      native_theme = browser->window()->GetNativeTheme();
+    }
+
+    if (!native_theme) {
+      // Find for WebContents hosted in a widget, but not directly in a
+      // Browser. e.g. Tab Search, Read Later.
+      views::Widget* widget = views::Widget::GetTopLevelWidgetForNativeView(
+          web_contents->GetContentNativeView());
+      if (widget) {
+        native_theme = widget->GetNativeTheme();
+      }
+    }
+  }
+
+  if (!native_theme) {
+    // Find for isolated WebContents, e.g. in tests.
+    // Or when |web_contents| is nullptr, because the renderer is not ready.
+    // TODO(crbug.com/40677117): Remove global accessor to NativeTheme.
+    native_theme = ui::NativeTheme::GetInstanceForNativeUi();
+  }
+
+  return native_theme;
+}
+
+const ui::ThemeProvider* GetThemeProviderDeprecated(
+    content::WebContents* web_contents) {
+  if (g_theme_provider_for_testing) {
+    return g_theme_provider_for_testing;
+  }
+
+  auto* browser_window =
+      BrowserWindow::FindBrowserWindowWithWebContents(web_contents);
+
+  if (browser_window) {
+    return browser_window->GetThemeProvider();
+  }
+
+  // Fallback 1: get the theme provider from the profile's associated browser.
+  // This is used in newly created tabs, e.g. NewTabPageUI, where theming is
+  // required before the WebContents is attached to a browser window.
+  // TODO(crbug.com/40823135): Remove this fallback by associating the
+  // WebContents during navigation.
+  Profile* profile =
+      Profile::FromBrowserContext(web_contents->GetBrowserContext());
+  const Browser* browser = chrome::FindBrowserWithProfile(profile);
+  if (browser) {
+    return browser->window()->GetThemeProvider();
+  }
+
+  // Fallback 2: get the theme provider from the last created browser.
+  // This is used in ChromeOS, where under multi-signin a browser window can
+  // be sent to another profile.
+  // TODO(crbug.com/40823135): Remove this fallback by associating the
+  // WebContents during navigation.
+  BrowserList* browser_list = BrowserList::GetInstance();
+  browser = browser_list->empty()
+                ? nullptr
+                : *std::prev(BrowserList::GetInstance()->end());
+  return browser ? browser->window()->GetThemeProvider() : nullptr;
+}
+
+void SetThemeProviderForTestingDeprecated(
+    const ui::ThemeProvider* theme_provider) {
+  g_theme_provider_for_testing = theme_provider;
+}
+
+}  // namespace webui

chrome/browser/ui/webui/webui_util_desktop.h

@@ -0,0 +1,37 @@
+// Copyright 2024 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_UI_WEBUI_WEBUI_UTIL_DESKTOP_H_
+#define CHROME_BROWSER_UI_WEBUI_WEBUI_UTIL_DESKTOP_H_
+
+namespace content {
+class WebContents;
+}
+
+namespace ui {
+class NativeTheme;
+class ThemeProvider;
+}  // namespace ui
+
+namespace webui {
+
+// These methods should not be used. Instead, browser-related state should be
+// passed from the owner of the WebUI instance to the WebUIController instance.
+// See LensOverlayController for one example of how to do this.
+// Returns whether WebContents should use dark mode colors depending on the
+// theme.
+ui::NativeTheme* GetNativeThemeDeprecated(content::WebContents* web_contents);
+
+// Returns the ThemeProvider instance associated with the given web contents.
+const ui::ThemeProvider* GetThemeProviderDeprecated(
+    content::WebContents* web_contents);
+
+// Sets a global theme provider that will be returned when calling
+// webui::GetThemeProviderDeprecated(). Used only for testing.
+void SetThemeProviderForTestingDeprecated(
+    const ui::ThemeProvider* theme_provider);
+
+}  // namespace webui
+
+#endif  // CHROME_BROWSER_UI_WEBUI_WEBUI_UTIL_DESKTOP_H_

chrome/test/BUILD.gn

@@ -10674,6 +10674,7 @@ if (!is_android) {
       "//chrome/browser/devtools",
       "//chrome/browser/profiles:profile",
       "//chrome/browser/ui",
+      "//chrome/browser/ui/webui",
       "//chrome/browser/web_applications",
       "//chrome/browser/web_applications:web_applications_test_support",
       "//chrome/common",

docs/ui/learn/bestpractices/colors.md

@@ -689,13 +689,13 @@ const ui::ThemeProvider* GetThemeProvider(content::WebContents* web_contents);
 void NTPResourceCache::CreateNewTabIncognitoCSS(
     const content::WebContents::Getter& wc_getter) {
   auto* web_contents = wc_getter.Run();
-  const ui::NativeTheme* native_theme = webui::GetNativeTheme(web_contents);
+  const ui::NativeTheme* native_theme = webui::GetNativeThemeDeprecated(web_contents);
   DCHECK(native_theme);
 
   // Requesting the incognito CSS is only done from within incognito browser
   // windows. The ThemeProvider associated with the requesting WebContents will
   // wrap the relevant incognito bits.
-  const ui::ThemeProvider* tp = webui::GetThemeProvider(web_contents);
+  const ui::ThemeProvider* tp = webui::GetThemeProviderDeprecated(web_contents);
   DCHECK(tp);
 
   ...