Enabled client side sampling for user metrics reporting.

chrome/browser/metrics/chrome_metrics_services_manager_client.h

Index: chrome/browser/metrics/chrome_metrics_services_manager_client.h
diff --git a/chrome/browser/metrics/chrome_metrics_services_manager_client.h b/chrome/browser/metrics/chrome_metrics_services_manager_client.h
index f79bb692e0a0fdc9e6ea18c6e33e8cbf857af055..51bfe205ad34fa1b82bb5d9aa6963f687102c95b 100644
--- a/chrome/browser/metrics/chrome_metrics_services_manager_client.h
+++ b/chrome/browser/metrics/chrome_metrics_services_manager_client.h
@@ -7,6 +7,7 @@
 
 #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"
@@ -19,6 +20,11 @@ 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 {