Add Synthetic Field Trial TS API

Bug: 394958637
Change-Id: I63dba2ef13866721e93b0a55c9eef96dda990184
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6303005
Reviewed-by: Erik Chen <erikchen@chromium.org>
Commit-Queue: Nick Birnie <birnie@google.com>
Cr-Commit-Position: refs/heads/main@{#1427373}

chrome/browser/glic/BUILD.gn

@@ -25,6 +25,7 @@ source_set("glic") {
     "glic_pref_names.h",
     "glic_profile_manager.h",
     "glic_settings_util.h",
+    "glic_synthetic_trial_manager.h",
     "glic_tab_data.h",
     "glic_tab_indicator_helper.h",
     "glic_ui.h",
@@ -47,9 +48,11 @@ source_set("glic") {
     "//chrome/browser/ui/browser_window:browser_window",
     "//chrome/browser/ui/tabs:tab_strip_model_observer",
     "//components/favicon/core:core",
+    "//components/metrics:metrics",
     "//components/optimization_guide/content/browser:browser",
     "//components/prefs",
     "//components/signin/public/identity_manager:identity_manager",
+    "//components/variations:variations",
     "//content/public/browser",
     "//pdf/mojom:mojom",
     "//ui/views:views",
@@ -96,6 +99,7 @@ source_set("impl") {
     "glic_screenshot_capturer.cc",
     "glic_screenshot_capturer.h",
     "glic_settings_util.cc",
+    "glic_synthetic_trial_manager.cc",
     "glic_tab_data.cc",
     "glic_tab_indicator_helper.cc",
     "glic_ui.cc",

chrome/browser/glic/glic.mojom

@@ -361,6 +361,13 @@ interface WebClientHandler {
   // Scrolls to and (optionally) highlights content specified by `params`.
   // Returns an error reason if the scroll fails, or null otherwise.
   ScrollTo(ScrollToParams params) => (ScrollToErrorReason? error_reason);
+
+  // Enrolls Chrome in the synthetic experiment group specified by
+  // trial_name.group_name. Enrollment will start when the API is called and end
+  // when Chrome closes.
+  SetSyntheticExperimentState(string trial_name,
+                              string group_name);
+
 };
 
 // State of the glic panel.

chrome/browser/glic/glic_keyed_service.h

@@ -15,6 +15,7 @@
 #include "chrome/browser/glic/glic_enums.h"
 #include "chrome/browser/glic/glic_focused_tab_manager.h"
 #include "chrome/browser/glic/glic_page_handler.h"
+#include "chrome/browser/glic/glic_synthetic_trial_manager.h"
 #include "components/keyed_service/core/keyed_service.h"
 
 class BrowserWindowInterface;
@@ -95,6 +96,11 @@ class GlicKeyedService : public KeyedService {
   void SetContextAccessIndicator(bool show);
   void NotifyWindowIntentToShow();
 
+  // Accessor for the GlicSyntheticTrialManager singleton. This exists as a
+  // singleton so that it may be shared across multiple profiles.
+  raw_ptr<GlicSyntheticTrialManager> synthetic_trial_manager() {
+    return GlicSyntheticTrialManager::GetInstance();
+  }
   // Callback for changes to focused tab data.
   using FocusedTabChangedCallback =
       base::RepeatingCallback<void(FocusedTabData)>;

chrome/browser/glic/glic_page_handler.cc

@@ -25,6 +25,7 @@
 #include "chrome/browser/glic/glic_keyed_service_factory.h"
 #include "chrome/browser/glic/glic_metrics.h"
 #include "chrome/browser/glic/glic_pref_names.h"
+#include "chrome/browser/glic/glic_synthetic_trial_manager.h"
 #include "chrome/browser/glic/glic_tab_data.h"
 #include "chrome/browser/glic/glic_web_client_access.h"
 #include "chrome/browser/glic/glic_window_controller.h"
@@ -407,6 +408,12 @@ class GlicWebClientHandler : public glic::mojom::WebClientHandler,
     annotation_manager_->ScrollTo(std::move(params), std::move(callback));
   }
 
+  void SetSyntheticExperimentState(const std::string& trial_name,
+                                   const std::string& group_name) override {
+    glic_service_->synthetic_trial_manager()->SetSyntheticExperimentState(
+        trial_name, group_name);
+  }
+
   // GlicWindowController::StateObserver implementation.
   void PanelStateChanged(const glic::mojom::PanelState& panel_state,
                          Browser* attached_browser) override {

chrome/browser/glic/glic_synthetic_trial_manager.cc

@@ -0,0 +1,96 @@
+// Copyright 2025 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/glic/glic_synthetic_trial_manager.h"
+
+#include <algorithm>
+#include <cstddef>
+#include <ranges>
+#include <string_view>
+#include <utility>
+#include <vector>
+
+#include "base/functional/bind.h"
+#include "base/logging.h"
+#include "base/memory/singleton.h"
+#include "base/metrics/histogram_functions.h"
+#include "chrome/browser/browser_process.h"
+#include "chrome/browser/metrics/chrome_metrics_service_accessor.h"
+#include "components/metrics/metrics_service.h"
+#include "components/variations/synthetic_trial_registry.h"
+
+namespace glic {
+
+// static
+GlicSyntheticTrialManager* GlicSyntheticTrialManager::GetInstance() {
+  return base::Singleton<GlicSyntheticTrialManager>::get();
+}
+
+GlicSyntheticTrialManager::GlicSyntheticTrialManager() {
+  metrics::MetricsService* metrics_service =
+      g_browser_process->metrics_service();
+  if (metrics_service) {
+    metrics_service->AddLogsObserver(this);
+  }
+}
+
+GlicSyntheticTrialManager::~GlicSyntheticTrialManager() {
+  metrics::MetricsService* metrics_service =
+      g_browser_process->metrics_service();
+  if (metrics_service) {
+    metrics_service->RemoveLogsObserver(this);
+  }
+}
+
+void GlicSyntheticTrialManager::SetSyntheticExperimentState(
+    const std::string& trial_name,
+    const std::string& group_name) {
+  // If already registered discard the logs if in a different group. This
+  // avoids combining logs from multiple groups from different profiles.
+  bool conflicting_group_registered =
+      synthetic_field_trial_groups_.count(trial_name) > 0 &&
+      synthetic_field_trial_groups_[trial_name] != group_name;
+
+  if (conflicting_group_registered) {
+    if (synthetic_field_trial_groups_[trial_name] != "MultiProfileDetected") {
+      base::UmaHistogramBoolean(
+          "Glic.ChromeClient.MultiProfileSyntheticTrialConflictDetected",
+          conflicting_group_registered);
+    }
+    ChromeMetricsServiceAccessor::RegisterSyntheticFieldTrial(
+        trial_name, "MultiProfileDetected",
+        variations::SyntheticTrialAnnotationMode::kCurrentLog);
+    synthetic_field_trial_groups_[trial_name] = "MultiProfileDetected";
+    // After contaminated logfile is uploaded we store the the most recently
+    // requested group to register the next created log file. If TrialA.Group1
+    // is reported then TrialA.Group2, then TrialA.Group3, then the next log cut
+    // will register TrialA.Group3.
+    staged_synthetic_field_trial_groups_[trial_name] = group_name;
+  } else {
+    ChromeMetricsServiceAccessor::RegisterSyntheticFieldTrial(
+        trial_name, group_name,
+        variations::SyntheticTrialAnnotationMode::kCurrentLog);
+    synthetic_field_trial_groups_[trial_name] = group_name;
+  }
+}
+
+void GlicSyntheticTrialManager::OnLogEvent(
+    metrics::MetricsLogsEventManager::LogEvent event,
+    std::string_view log_hash,
+    std::string_view message) {
+  if (event == metrics::MetricsLogsEventManager::LogEvent::kLogCreated &&
+      !staged_synthetic_field_trial_groups_.empty()) {
+    // Remove all elements from synthetic_field_trial_groups_ that have
+    // entries in staged_synthetic_field_trial_groups_ with the same
+    // trial_name.
+    for (const auto& [trial, group] : staged_synthetic_field_trial_groups_) {
+      ChromeMetricsServiceAccessor::RegisterSyntheticFieldTrial(
+          trial, group, variations::SyntheticTrialAnnotationMode::kCurrentLog);
+      synthetic_field_trial_groups_[trial] = group;
+    }
+    staged_synthetic_field_trial_groups_ = {};
+  }
+}
+
+}  // namespace glic

chrome/browser/glic/glic_synthetic_trial_manager.h

@@ -0,0 +1,57 @@
+// Copyright 2025 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_GLIC_GLIC_SYNTHETIC_TRIAL_MANAGER_H_
+#define CHROME_BROWSER_GLIC_GLIC_SYNTHETIC_TRIAL_MANAGER_H_
+
+#include <string>
+#include <vector>
+
+#include "base/functional/callback_forward.h"
+#include "base/memory/weak_ptr.h"
+#include "components/metrics/metrics_logs_event_manager.h"
+#include "components/metrics/metrics_service.h"
+#include "components/variations/synthetic_trial_registry.h"
+
+namespace glic {
+
+class GlicSyntheticTrialManager : metrics::MetricsLogsEventManager::Observer {
+ public:
+  static GlicSyntheticTrialManager* GetInstance();
+  GlicSyntheticTrialManager();
+
+  GlicSyntheticTrialManager(const GlicSyntheticTrialManager&) = delete;
+  GlicSyntheticTrialManager& operator=(const GlicSyntheticTrialManager&) =
+      delete;
+
+  ~GlicSyntheticTrialManager() override;
+
+  // Used by the web client to enroll Chrome in the specified synthetic trial
+  // group. If a conflicting group is already registered by another profile
+  // than we instead register into a new group called `MultiProfileDetected` to
+  // indicate the log file is corrupted. At this point we stage the requested
+  // group for enrollment when the next log file is created.
+  void SetSyntheticExperimentState(const std::string& trial_name,
+                                   const std::string& group_name);
+
+  // metrics::MetricsLogsEventManager::Observer:
+  void OnLogEvent(metrics::MetricsLogsEventManager::LogEvent event,
+                  std::string_view log_hash,
+                  std::string_view message) override;
+  void OnLogCreated(
+      std::string_view log_hash,
+      std::string_view log_data,
+      std::string_view log_timestamp,
+      metrics::MetricsLogsEventManager::CreateReason reason) override {}
+
+ private:
+  std::map<std::string, std::string> synthetic_field_trial_groups_;
+  std::map<std::string, std::string> staged_synthetic_field_trial_groups_;
+
+  base::WeakPtrFactory<GlicSyntheticTrialManager> weak_ptr_factory_{this};
+};
+
+}  // namespace glic
+
+#endif  // CHROME_BROWSER_GLIC_GLIC_SYNTHETIC_TRIAL_MANAGER_H_

chrome/browser/metrics/chrome_metrics_service_accessor.h

@@ -12,10 +12,15 @@
 #include "base/gtest_prod_util.h"
 #include "build/build_config.h"
 #include "chrome/browser/metrics/metrics_reporting_state.h"
+#include "chrome/common/buildflags.h"
 #include "components/metrics/metrics_service_accessor.h"
 #include "components/variations/synthetic_trials.h"
 #include "ppapi/buildflags/buildflags.h"
 
+#if BUILDFLAG(ENABLE_GLIC)
+#include "chrome/browser/glic/glic_synthetic_trial_manager.h"
+#endif
+
 #if BUILDFLAG(ENABLE_PPAPI)
 #include "chrome/common/ppapi_metrics.mojom.h"
 #endif
@@ -175,6 +180,9 @@ class ChromeMetricsServiceAccessor : public metrics::MetricsServiceAccessor {
   friend class ChromeBrowserMainExtraPartsGpu;
   friend class Browser;
   friend class BrowserProcessImpl;
+#if BUILDFLAG(ENABLE_GLIC)
+  friend class glic::GlicSyntheticTrialManager;
+#endif
   friend class OptimizationGuideKeyedService;
   friend class WebUITabStripFieldTrial;
   friend class feed::FeedServiceDelegateImpl;

chrome/browser/resources/glic/glic_api/glic_api.ts

@@ -334,6 +334,13 @@ export declare interface GlicBrowserHost {
    * @throws {ScrollToError} on failure.
    */
   scrollTo?(params: ScrollToParams): Promise<void>;
+
+  /**
+   * Enrolls the Chrome client in the synthetic experiment group specified by
+   * trial_name.group_name. Enrollment will only start when the API is called
+   * and end when Chrome closes.
+   */
+  setSyntheticExperimentState?(trialName: string, groupName: string): void;
 }
 
 /** Holds optional parameters for `GlicBrowserHost#resizeWindow`. */

chrome/browser/resources/glic/glic_api_impl/glic_api_client.ts

@@ -372,6 +372,11 @@ class GlicBrowserHostImpl implements GlicBrowserHost {
   scrollTo(params: ScrollToParams): Promise<void> {
     return this.sender.requestWithResponse('glicBrowserScrollTo', {params});
   }
+
+  setSyntheticExperimentState(trialName: string, groupName: string): void {
+    this.sender.requestNoResponse(
+        'glicBrowserSetSyntheticExperimentState', {trialName, groupName});
+  }
 }
 
 class GlicBrowserHostMetricsImpl implements GlicBrowserHostMetrics {

chrome/browser/resources/glic/glic_api_impl/glic_api_host.ts

@@ -477,6 +477,14 @@ class HostMessageHandler implements HostMessageHandlerInterface {
     }
     return {};
   }
+
+  glicBrowserSetSyntheticExperimentState(request: {
+    trialName: string,
+    groupName: string,
+  }) {
+    return this.handler.setSyntheticExperimentState(
+        request.trialName, request.groupName);
+  }
 }
 
 export class GlicApiHost implements PostMessageRequestHandler {

chrome/browser/resources/glic/glic_api_impl/request_types.ts

@@ -142,6 +142,12 @@ export declare interface HostRequestTypes {
   glicBrowserScrollTo: {
     request: {params: ScrollToParams},
   };
+  glicBrowserSetSyntheticExperimentState: {
+    request: {
+      trialName: string,
+      groupName: string,
+    },
+  };
 }
 
 // Types of requests to the GlicWebClient.

chrome/test/data/webui/glic/test_client/index.html

@@ -277,6 +277,15 @@ found in the LICENSE file.
   </div>
   <button id="scrollToBn" style="margin-top: 12px;">Scroll!</button>
 </div>
+<div class="section">
+  <h1>Set Synthetic Experiment</h1>
+  <label for="trialName">Trial Name:</label>
+  <input type="text" id="trialName" name="trialName"><br><br>
+  <label for="groupName">Group Name:</label>
+  <input type="text" id="groupName" name="groupName"><br><br>
+  <button id="setExperiment">Set Experiment</button>
+  <span id="setExperimentStatus"></span>
+</div>
 <br />
 <div id="status"></div>
 </div>

chrome/test/data/webui/glic/test_client/test_client.ts

@@ -70,6 +70,10 @@ interface PageElementTypes {
   fileDropList: HTMLDivElement;
   showDirectoryPicker: HTMLButtonElement;
   failInitializationCheckbox: HTMLInputElement;
+  setExperiment: HTMLButtonElement;
+  trialName: HTMLInputElement;
+  groupName: HTMLInputElement;
+  setExperimentStatus: HTMLSpanElement;
 }
 
 const $: PageElementTypes = new Proxy({}, {
@@ -638,6 +642,14 @@ window.addEventListener('load', () => {
       $.desktopScreenshotErrorReason!.innerText = `Caught error: ${error}`;
     }
   });
+  $.setExperiment.addEventListener('click', async () => {
+    const trialName = $.trialName.value;
+    const groupName = $.groupName.value;
+    $.setExperimentStatus!.innerText +=
+        `\nSetting experiment: ${trialName} ${groupName}`;
+    await getBrowser()!.setSyntheticExperimentState!(trialName, groupName);
+    $.setExperimentStatus!.innerText += '\nExperiment State Set.';
+  });
 });
 
 function readStream(stream: ReadableStream<Uint8Array>): Promise<Uint8Array> {

tools/metrics/histograms/metadata/glic/histograms.xml

@@ -32,6 +32,20 @@ chromium-metrics-reviews@google.com.
   </summary>
 </histogram>
 
+<histogram name="Glic.ChromeClient.MultiProfileSyntheticTrialConflictDetected"
+    enum="BooleanEnabled" expires_after="2026-01-15">
+  <owner>birnie@chromium.org</owner>
+  <owner>carlosk@chromium.org</owner>
+  <summary>
+    Recorded when different Chrome profiles using glic attempt to register
+    conflicting synthetic field trial groups in the same log file. This should
+    only happen on multi profile installs that use glic on different profiles in
+    quick succession. When analyzing metrics from a synthetic field trial this
+    histogram will allow us to create custom queries to filter out users who may
+    have contaminated logs from multiple profiles.
+  </summary>
+</histogram>
+
 <histogram name="Glic.EntryPoint.Impression" enum="GlicEntryPointImpression"
     expires_after="2026-01-15">
   <owner>erikchen@chromium.org</owner>