Implement EnumFonts() in pdf/pdfium/pdfium_font_win.cc

Add the ability for the PDF Viewer to tell PDFium about the fonts on the
system on Windows. This allows PDFium to make better decisions when
mapping fonts.

Bug: 381126164
Low-Coverage-Reason: COVERAGE_UNDERREPORTED see patchset 3 try jobs.
Change-Id: Ia28988b8e678ac1e71dddccea7600534b2ea2607
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6075232
Reviewed-by: Alex Gough <ajgo@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1393977}

pdf/pdfium/pdfium_font_win.cc

@@ -13,6 +13,7 @@
 #include "base/containers/contains.h"
 #include "base/containers/fixed_flat_map.h"
 #include "base/containers/flat_map.h"
+#include "base/feature_list.h"
 #include "base/logging.h"
 #include "base/no_destructor.h"
 #include "base/sequence_checker.h"
@@ -59,6 +60,13 @@ std::string GetSubstFont(const std::string& face) {
   return face;
 }
 
+// Kill switch in case this goes horribly wrong.
+// TODO(crbug.com/381126164): Remove after this lands safely in a Stable
+// release.
+BASE_FEATURE(kPdfEnumFontsWin,
+             "PdfEnumFontsWin",
+             base::FEATURE_ENABLED_BY_DEFAULT);
+
 // Maps font description and charset to `FontId` as requested by PDFium, with
 // `FontId` as an opaque type that PDFium works with. Based on the `FontId`,
 // PDFium can read from the font files using GetFontData(). Properly frees the
@@ -73,6 +81,28 @@ class SkiaFontMapper {
 
   ~SkiaFontMapper() = delete;
 
+  void EnumFonts(FPDF_SYSFONTINFO* sysfontinfo, void* mapper) {
+    if (!base::FeatureList::IsEnabled(kPdfEnumFontsWin)) {
+      return;
+    }
+
+    const int count = manager_->countFamilies();
+    for (int i = 0; i < count; ++i) {
+      SkString family;
+      manager_->getFamilyName(i, &family);
+      // Skia does not make any guarantees about whether `family` can be empty
+      // or not.
+      // PDFium does not check if FPDF_AddInstalledFont() got an empty string.
+      // Do an explicit check here to make sure the two sides play nicely
+      // together.
+      if (!family.isEmpty()) {
+        // It may be better to pick a more accurate character set value, but
+        // this is good enough for now.
+        FPDF_AddInstalledFont(mapper, family.c_str(), FXFONT_DEFAULT_CHARSET);
+      }
+    }
+  }
+
   // Returns a handle to the font mapped based on `desc`, for use
   // as the `font_id` in GetFontData() and DeleteFont() below. Returns nullptr
   // on failure.
@@ -316,6 +346,16 @@ SkiaFontMapper& GetSkiaFontMapper() {
   return *mapper;
 }
 
+void EnumFonts(FPDF_SYSFONTINFO* sysfontinfo, void* mapper) {
+  // Exit early if PDFium was specifically configured in `kNoMapping` mode.
+  if (PDFiumEngine::GetFontMappingMode() != FontMappingMode::kBlink) {
+    CHECK_EQ(PDFiumEngine::GetFontMappingMode(), FontMappingMode::kNoMapping);
+    return;
+  }
+
+  GetSkiaFontMapper().EnumFonts(sysfontinfo, mapper);
+}
+
 // Note: `exact` is obsolete.
 void* MapFont(FPDF_SYSFONTINFO*,
               int weight,
@@ -349,7 +389,7 @@ void DeleteFont(FPDF_SYSFONTINFO*, void* font_id) {
 
 FPDF_SYSFONTINFO g_font_info = {.version = 1,
                                 .Release = nullptr,
-                                .EnumFonts = nullptr,
+                                .EnumFonts = EnumFonts,
                                 .MapFont = MapFont,
                                 .GetFont = nullptr,
                                 .GetFontData = GetFontData,