Enabled client side sampling for user metrics reporting.

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;
 }
 
+// Metrics reporting feature. This feature, along with user consent, controls if
+// recording and reporting are enabled. If the feature is enabled, but no
+// consent is given, then there will be no recording or reporting.
+extern const base::Feature kMetricsReportingFeature;

[Alexei Svitkine (slow), 2016/07/19 15:23:59]

If this will not be used outside the file, just put it in the anon namespace in
the file and don't declare it in the header.

[jwd, 2016/07/19 21:21:49]

It's going to be used by a metrics provider for reporting the sampling rate.

+
 // Provides a //chrome-specific implementation of MetricsServicesManagerClient.
 class ChromeMetricsServicesManagerClient
     : public metrics_services_manager::MetricsServicesManagerClient {
  public:
   explicit ChromeMetricsServicesManagerClient(PrefService* local_state);
   ~ChromeMetricsServicesManagerClient() override;
 
  private:
   // This is defined as a member class to get access to
   // ChromeMetricsServiceAccessor through ChromeMetricsServicesManagerClient's
@@ skipping 29 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_