Add synthetic field trial for Optimization Guide-enabled users

Bug: 1115698
Change-Id: I03e7514d22c7a4f8592793de1e69202b0356565a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2352038Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Michael Crouse <mcrouse@chromium.org>
Commit-Queue: Sophie Chang <sophiechang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#797487}

chrome/browser/metrics/chrome_metrics_service_accessor.h

@@ -120,6 +120,7 @@ class ChromeMetricsServiceAccessor : public metrics::MetricsServiceAccessor {
   friend class NavigationMetricsRecorder;
   friend class ChromeBrowserMainExtraPartsGpu;
   friend class Browser;
+  friend class OptimizationGuideKeyedService;
 
 #if defined(OS_CHROMEOS)
   friend class ChromeCameraAppUIDelegate;

chrome/browser/optimization_guide/optimization_guide_keyed_service.cc

@@ -10,6 +10,7 @@
 #include "base/metrics/histogram_functions.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/optional.h"
+#include "chrome/browser/metrics/chrome_metrics_service_accessor.h"
 #include "chrome/browser/optimization_guide/optimization_guide_hints_manager.h"
 #include "chrome/browser/optimization_guide/optimization_guide_navigation_data.h"
 #include "chrome/browser/optimization_guide/optimization_guide_session_statistic.h"
@@ -111,8 +112,12 @@ void OptimizationGuideKeyedService::Initialize(
 
   Profile* profile = Profile::FromBrowserContext(browser_context_);
   top_host_provider_ = GetTopHostProviderIfUserPermitted(browser_context_);
+  bool optimization_guide_fetching_enabled = top_host_provider_ != nullptr;
   UMA_HISTOGRAM_BOOLEAN("OptimizationGuide.RemoteFetchingEnabled",
-                        top_host_provider_ != nullptr);
+                        optimization_guide_fetching_enabled);
+  ChromeMetricsServiceAccessor::RegisterSyntheticFieldTrial(
+      "SyntheticOptimizationGuideRemoteFetching",
+      optimization_guide_fetching_enabled ? "Enabled" : "Disabled");
   scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory =
       content::BrowserContext::GetDefaultStoragePartition(profile)
           ->GetURLLoaderFactoryForBrowserProcess();

chrome/browser/optimization_guide/optimization_guide_keyed_service_browsertest.cc

@@ -29,6 +29,8 @@
 #include "components/prefs/pref_service.h"
 #include "components/previews/core/previews_switches.h"
 #include "components/ukm/test_ukm_recorder.h"
+#include "components/variations/active_field_trials.h"
+#include "components/variations/hashing.h"
 #include "content/public/browser/navigation_handle.h"
 #include "content/public/test/browser_test.h"
 #include "content/public/test/browser_test_utils.h"
@@ -242,6 +244,19 @@ class OptimizationGuideKeyedServiceBrowserTest
     consumer_->set_callback(std::move(callback));
   }
 
+  // Returns whether the synthetic trial |trial_name| has been logged and is in
+  // the |trial_group| for the trial.
+  bool IsInSyntheticTrialGroup(const std::string& trial_name,
+                               const std::string& trial_group) {
+    std::vector<std::string> synthetic_trials;
+    variations::GetSyntheticTrialGroupIdsAsString(&synthetic_trials);
+    std::string expected_entry =
+        base::StringPrintf("%x-%x", variations::HashName(trial_name),
+                           variations::HashName(trial_group));
+    return std::find(synthetic_trials.begin(), synthetic_trials.end(),
+                     expected_entry) != synthetic_trials.end();
+  }
+
   // Returns the last decision from the CanApplyOptimization() method seen by
   // the consumer of the OptimizationGuideKeyedService.
   optimization_guide::OptimizationGuideDecision
@@ -301,6 +316,8 @@ IN_PROC_BROWSER_TEST_F(OptimizationGuideKeyedServiceBrowserTest,
 #if !defined(OS_CHROMEOS)
   histogram_tester()->ExpectUniqueSample(
       "OptimizationGuide.RemoteFetchingEnabled", false, 1);
+  EXPECT_TRUE(IsInSyntheticTrialGroup(
+      "SyntheticOptimizationGuideRemoteFetching", "Disabled"));
 #endif
 }
 
@@ -595,6 +612,8 @@ IN_PROC_BROWSER_TEST_F(
 #if !defined(OS_CHROMEOS)
   histogram_tester()->ExpectUniqueSample(
       "OptimizationGuide.RemoteFetchingEnabled", true, 1);
+  EXPECT_TRUE(IsInSyntheticTrialGroup(
+      "SyntheticOptimizationGuideRemoteFetching", "Enabled"));
 #endif
 }
 
@@ -627,5 +646,7 @@ IN_PROC_BROWSER_TEST_F(OptimizationGuideKeyedServiceCommandLineOverridesTest,
 #if !defined(OS_CHROMEOS)
   histogram_tester()->ExpectUniqueSample(
       "OptimizationGuide.RemoteFetchingEnabled", true, 1);
+  EXPECT_TRUE(IsInSyntheticTrialGroup(
+      "SyntheticOptimizationGuideRemoteFetching", "Enabled"));
 #endif
 }