Add histograms for data usage

chrome/browser/android/data_usage/external_data_use_observer.cc

 // 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.
 
 #include "chrome/browser/android/data_usage/external_data_use_observer.h"
 
 #include <utility>
 
 #include "base/containers/hash_tables.h"
 #include "base/message_loop/message_loop.h"
@@ skipping 187 matching lines @@
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(!last_data_report_submitted_ticks_.is_null());
 
   if (success) {
     RecordDataUsageReportSubmission(DATAUSAGE_REPORT_SUBMISSION_SUCCESSFUL,
                                     pending_report_bytes_);
   } else {
     RecordDataUsageReportSubmission(DATAUSAGE_REPORT_SUBMISSION_FAILED,
                                     pending_report_bytes_);
   }
+  UMA_HISTOGRAM_TIMES(

[Raj, 2016/01/13 23:33:51]

Here again, the duration includes 2 thread hops.
Should we need to only log pure report submission timing ?
Or thread hop is negligible ? 

[tbansal1, 2016/01/14 06:59:55]

Delay due to thread hop can sometimes be large. I think here it is okay to
include thread hop because EDUO can submit next report only when the previous
report callback has come back. So, we are measuring the right metric.

In the other place, you were adding an extra unnecessary thread hop just for
measuring purpose, so that was not measuring the right metric.

+      "DataUsage.Perf.ReportSubmissionDuration",
+      base::TimeTicks::Now() - last_data_report_submitted_ticks_);
 
   last_data_report_submitted_ticks_ = base::TimeTicks();
   pending_report_bytes_ = 0;
 
   SubmitBufferedDataUseReport(false);
 }
 
+void ExternalDataUseObserver::OnFetchMatchingRulesDone() const {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(!last_matching_rules_fetch_time_.is_null());
+  UMA_HISTOGRAM_TIMES("DataUsage.Perf.MatchingRuleFetchDuration",
+                      base::TimeTicks::Now() - last_matching_rules_fetch_time_);
+}
+
 #if defined(OS_ANDROID)
 void ExternalDataUseObserver::OnApplicationStateChange(
     base::android::ApplicationState new_state) {
   DCHECK(thread_checker_.CalledOnValidThread());
   if (new_state == base::android::APPLICATION_STATE_HAS_PAUSED_ACTIVITIES)
     SubmitBufferedDataUseReport(true);
 }
 #endif
 
 void ExternalDataUseObserver::OnDataUse(const data_usage::DataUse& data_use) {
@@ skipping 213 matching lines @@
   size_t hash = 1;
   hash = hash * 23 + hash_function(k.label);
   hash = hash * 43 + k.connection_type;
   hash = hash * 83 + hash_function(k.mcc_mnc);
   return hash;
 }
 
 }  // namespace android
 
 }  // namespace chrome