Adding local field trial for metrics/crash reports sampling.

chrome/browser/chrome_browser_field_trials.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chrome_browser_field_trials.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/feature_list.h"
 #include "base/files/file_util.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_base.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/persistent_histogram_allocator.h"
 #include "base/path_service.h"
 #include "base/strings/string_util.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
 #include "chrome/browser/metrics/chrome_metrics_service_client.h"
+#include "chrome/browser/metrics/chrome_metrics_services_manager_client.h"
 #include "chrome/browser/tracing/background_tracing_field_trial.h"
+#include "chrome/common/channel_info.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
 #include "components/metrics/metrics_pref_names.h"
 #include "components/variations/variations_associated_data.h"
+#include "components/version_info/version_info.h"
 
 #if defined(OS_ANDROID)
 #include "chrome/browser/chrome_browser_field_trials_mobile.h"
 #else
 #include "chrome/browser/chrome_browser_field_trials_desktop.h"
 #endif
 
 namespace {
 
 // Check for feature enabling the use of persistent histogram storage and
@@ skipping 68 matching lines @@
                             CREATE_ALLOCATOR_RESULTS);
   if (!allocator)
     return;
 
   // Create tracking histograms for the allocator and record storage file.
   allocator->CreateTrackingHistograms(
       ChromeMetricsServiceClient::kBrowserMetricsName);
   allocator->SetPersistentLocation(active_file);
 }
 
+// Create a field trial to control metrics/crash sampling for Stable on
+// Windows/Android if no variations seed was applied.
+void CreateFallbackSamplingTrialIfNeeded(bool has_seed,
+                                         base::FeatureList* feature_list) {
+#if defined(OS_WIN) || defined(OS_ANDROID)
+  // Only create the fallback trial if there isn't already a variations seed
+  // being applied. This should occur during first run when first-run variations
+  // isn't supported. It's assumed that, if there is a seed, then it either
+  // contains the relavent study, or is intentionally omitted, so no fallback is
+  // needed.
+  if (has_seed)
+    return;
+
+  // Sampling is only supported on Stable.
+  if (chrome::GetChannel() != version_info::Channel::STABLE)
+    return;
+
+  ChromeMetricsServicesManagerClient::CreateFallbackSamplingTrial(feature_list);
+#endif  // defined(OS_WIN) || defined(OS_ANDROID)
+}
+
 }  // namespace
 
 ChromeBrowserFieldTrials::ChromeBrowserFieldTrials(
     const base::CommandLine& parsed_command_line)
     : parsed_command_line_(parsed_command_line) {
 }
 
 ChromeBrowserFieldTrials::~ChromeBrowserFieldTrials() {
 }
 
 void ChromeBrowserFieldTrials::SetupFieldTrials() {
   // Field trials that are shared by all platforms.
   InstantiateDynamicTrials();
 
 #if defined(OS_ANDROID)
   chrome::SetupMobileFieldTrials(parsed_command_line_);
 #else
   chrome::SetupDesktopFieldTrials(parsed_command_line_);
 #endif
 }
 
+void ChromeBrowserFieldTrials::SetupFeatureControllingFieldTrials(
+    bool has_seed,
+    base::FeatureList* feature_list) {
+  CreateFallbackSamplingTrialIfNeeded(has_seed, feature_list);
+}
+
 void ChromeBrowserFieldTrials::InstantiateDynamicTrials() {
   // Persistent histograms must be enabled as soon as possible.
   InstantiatePersistentHistograms();
   tracing::SetupBackgroundTracingFieldTrial();
 }