Add histograms for data usage

chrome/browser/android/data_usage/external_data_use_observer_bridge.h

Index: chrome/browser/android/data_usage/external_data_use_observer_bridge.h
diff --git a/chrome/browser/android/data_usage/external_data_use_observer_bridge.h b/chrome/browser/android/data_usage/external_data_use_observer_bridge.h
index 2727c4074901f4ee9a56f3fd69406092ca6f2bda..9611f907fc6a2ff3f438f922a32f5e8fc56a9905 100644
--- a/chrome/browser/android/data_usage/external_data_use_observer_bridge.h
+++ b/chrome/browser/android/data_usage/external_data_use_observer_bridge.h
@@ -21,6 +21,7 @@
 namespace base {
 class SingleThreadTaskRunner;
 class Time;
+class TimeTicks;
 }
 
 namespace chrome {
@@ -50,7 +51,7 @@ class ExternalDataUseObserverBridge {
   // Fetches matching rules from Java. Returns result asynchronously via
   // FetchMatchingRulesDone. FetchMatchingRules should not be called if a
   // fetch to matching rules is already in progress.
-  void FetchMatchingRules() const;
+  void FetchMatchingRules();
 
   // Called by Java when new matching rules have been fetched.
   // |app_package_name| is the package name of the app that should be matched.
@@ -101,6 +102,9 @@ class ExternalDataUseObserverBridge {
   // |data_use_tab_model_| is notified of the matching rules on UI thread.
   base::WeakPtr<DataUseTabModel> data_use_tab_model_;
 
+  // The time of request when the matching rules are fetched for the first time.
+  base::TimeTicks matching_rules_first_fetch_time_;
+
   // |io_task_runner_| accesses ExternalDataUseObserver members on IO thread.
   scoped_refptr<base::SingleThreadTaskRunner> io_task_runner_;