Add histograms for ExternalDataUseObserver

chrome/browser/android/data_usage/external_data_use_observer.h

Index: chrome/browser/android/data_usage/external_data_use_observer.h
diff --git a/chrome/browser/android/data_usage/external_data_use_observer.h b/chrome/browser/android/data_usage/external_data_use_observer.h
index 30f6e6aed57e83ac9cfa3f561f6430167a99bc8c..3c3a2a69bb364ca33ec8ca9dffbb3486b86aa09a 100644
--- a/chrome/browser/android/data_usage/external_data_use_observer.h
+++ b/chrome/browser/android/data_usage/external_data_use_observer.h
@@ -103,6 +103,7 @@ class ExternalDataUseObserver : public data_usage::DataUseAggregator::Observer {
  private:
   friend class DataUseTabModelTest;
   friend class ExternalDataUseObserverTest;
+  FRIEND_TEST_ALL_PREFIXES(ExternalDataUseObserverTest, DataUseReportTimedOut);
   FRIEND_TEST_ALL_PREFIXES(ExternalDataUseObserverTest, SingleRegex);
   FRIEND_TEST_ALL_PREFIXES(ExternalDataUseObserverTest, TwoRegex);
   FRIEND_TEST_ALL_PREFIXES(ExternalDataUseObserverTest, MultipleRegex);
@@ -278,8 +279,15 @@ class ExternalDataUseObserver : public data_usage::DataUseAggregator::Observer {
   // True if callback from |FetchMatchingRulesDone| is currently pending.
   bool matching_rules_fetch_pending_;
 
-  // True if callback from |SubmitDataUseReportCallback| is currently pending.
-  bool submit_data_report_pending_;
+  // Time when the currently pending data use report was submitted.
+  // |last_data_report_submitted_| is null if no data use report is currently

[sclittle, 2015/12/02 19:07:54]

The NULL timeticks is a valid, real time; it shouldn't be used as a sentinel
value like this. You'll probably want to keep the bool you had before.

see
https://code.google.com/p/chromium/codesearch#chromium/src/base/time/time.h&l...

[tbansal1, 2015/12/03 03:19:45]

That applies only when doing Maths with TimeTicks. e.g., TimeTicks1 + TimeDelta
= TimeTicks2. It is possible that TimeTicks2 is 0.
But it is guaranteed that if TimeTicks has been initialized (without maths
operations), then it would have non null value.

+  // pending.
+  base::TimeTicks last_data_report_submitted_;

[sclittle, 2015/12/02 19:07:54]

nit: Name this so that it's obvious it's a point in time, e.g.
last_data_report_submitted_ticks_ or something.

[tbansal1, 2015/12/03 03:19:45]

Done.

+
+  // |pending_report_bytes_| is the total byte count in the data use report that
+  // is currently pending. |pending_report_bytes_| is 0 if no data use report is

[sclittle, 2015/12/02 19:07:54]

FYI: Be careful here - the DataUseAggregator could pass you DataUse objects with
both tx_bytes and rx_bytes of 0. It's fine to avoid submitting reports that are
0 bytes, but those will need to be filtered out right before reporting them.

[tbansal1, 2015/12/03 03:19:45]

Added an early return statement to filter out reports that have 0 bytes. Also,
changed the comment. Done.

+  // currently pending.
+  int64_t pending_report_bytes_;
 
   // Contains matching rules.
   std::vector<scoped_ptr<MatchingRule>> matching_rules_;
@@ -316,6 +324,10 @@ class ExternalDataUseObserver : public data_usage::DataUseAggregator::Observer {
   // submitted.
   const int64_t data_use_report_min_bytes_;
 
+  // If a data use report is pending for more than |data_report_submit_timeout_|
+  // duration, it is considered as timed out.
+  const base::TimeDelta data_report_submit_timeout_;
+
   base::ThreadChecker thread_checker_;
 
   // |io_weak_factory_| and |ui_weak_factory_| are used for posting tasks on the