Adding local field trial for metrics/crash reports sampling.

chrome/browser/metrics/chrome_metrics_services_manager_client.h

 // Copyright 2015 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.
 
 #ifndef CHROME_BROWSER_METRICS_CHROME_METRICS_SERVICES_MANAGER_CLIENT_H_
 #define CHROME_BROWSER_METRICS_CHROME_METRICS_SERVICES_MANAGER_CLIENT_H_
 
 #include <memory>
 
 #include "base/feature_list.h"
 #include "base/macros.h"
 #include "base/threading/thread_checker.h"
 #include "chrome/browser/safe_browsing/safe_browsing_service.h"
 #include "components/metrics_services_manager/metrics_services_manager_client.h"
 
 class PrefService;
 
 namespace metrics {
 class EnabledStateProvider;
 class MetricsStateManager;
 }
 
 // Provides a //chrome-specific implementation of MetricsServicesManagerClient.
 class ChromeMetricsServicesManagerClient
     : public metrics_services_manager::MetricsServicesManagerClient {
  public:
   explicit ChromeMetricsServicesManagerClient(PrefService* local_state);
   ~ChromeMetricsServicesManagerClient() override;
 
+  // Unconditionally attempts to create a field trial to control client side
+  // metrics/crash sampling to use as a fallback when one hasn't been
+  // provided. This is expected to occur on first-run on platforms that don't
+  // have first-run variations support. This should only be called when there is
+  // no existing field trial controlling the sampling feature, and on the
+  // correct platform and channel.
+  static void CreateFallbackSamplingTrial(base::FeatureList* feature_list);
+
   // Determines if this client is eligible to send metrics. If they are, and
   // there was user consent, then metrics and crashes would be reported.
   static bool IsClientInSample();
 
   // Gets the sample rate for in-sample clients. If the sample rate is not
   // defined, returns false, and |rate| is unchanged, otherwise returns true,
   // and |rate| contains the sample rate. If the client isn't in-sample, the
   // sample rate is undefined. It is also undefined for clients that are not
   // eligible for sampling.
   static bool GetSamplingRatePerMille(int* rate);
@@ skipping 38 matching lines @@
   PrefService* local_state_;
 
   // Subscription to SafeBrowsing service state changes.
   std::unique_ptr<safe_browsing::SafeBrowsingService::StateSubscription>
       sb_state_subscription_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeMetricsServicesManagerClient);
 };
 
 #endif  // CHROME_BROWSER_METRICS_CHROME_METRICS_SERVICES_MANAGER_CLIENT_H_