Implement UMA log throttling for cellular connections

components/metrics/metrics_service.h

Index: components/metrics/metrics_service.h
diff --git a/components/metrics/metrics_service.h b/components/metrics/metrics_service.h
index ce4102b8dfa36408fe037bd6772184d759a48a4e..f02df4bcabf1e4f285fb029ec3f41eea92f14d44 100644
--- a/components/metrics/metrics_service.h
+++ b/components/metrics/metrics_service.h
@@ -27,6 +27,7 @@
 #include "base/time/time.h"
 #include "build/build_config.h"
 #include "components/metrics/clean_exit_beacon.h"
+#include "components/metrics/data_use_tracker.h"
 #include "components/metrics/metrics_log.h"
 #include "components/metrics/metrics_log_manager.h"
 #include "components/metrics/metrics_provider.h"
@@ -214,6 +215,10 @@ class MetricsService : public base::HistogramFlattener {
   // Pushes a log that has been generated by an external component.
   void PushExternalLog(const std::string& log);
 
+  // Returns a callback to data use pref updating function which can be called
+  // from any thread, but this function should be called on UI thread.
+  UpdateUsagePrefCallbackType GetDataUseForwardingCallback();
+
  protected:
   // Exposed for testing.
   MetricsLogManager* log_manager() { return &log_manager_; }
@@ -468,7 +473,7 @@ class MetricsService : public base::HistogramFlattener {
   // Execution phase the browser is in.
   static ExecutionPhase execution_phase_;
 
-  // Reduntant marker to check that we completed our shutdown, and set the
+  // Redundant marker to check that we completed our shutdown, and set the
   // exited-cleanly bit in the prefs.
   static ShutdownCleanliness clean_shutdown_status_;
 
@@ -477,6 +482,9 @@ class MetricsService : public base::HistogramFlattener {
                            PermutedEntropyCacheClearedWhenLowEntropyReset);
   FRIEND_TEST_ALL_PREFIXES(MetricsServiceTest, RegisterSyntheticTrial);
 
+  // Pointer used for obtaining data use pref updater callback on above layers.
+  scoped_ptr<DataUseTracker> data_use_tracker_;
+
   // Weak pointers factory used to post task on different threads. All weak
   // pointers managed by this factory have the same lifetime as MetricsService.
   base::WeakPtrFactory<MetricsService> self_ptr_factory_;