Add histograms for observing UMA throttling effect.

components/metrics/metrics_service.cc

 // Copyright 2014 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.
 
 //------------------------------------------------------------------------------
 // Description of the life cycle of a instance of MetricsService.
 //
 //  OVERVIEW
 //
 // A MetricsService instance is typically created at application startup.  It is
@@ skipping 864 matching lines @@
     // Just tell the scheduler it was uploaded and wait for the next log
     // interval.
     scheduler_->UploadFinished(true, log_manager_.has_unsent_logs());
     return;
   }
   if (!log_manager_.has_staged_log())
     log_manager_.StageNextLogForUpload();
 
   // Proceed to stage the log for upload if log size satisfies cellular log
   // upload constrains.
+  bool upload_canceled = false;
   if (client_->IsUMACellularUploadLogicEnabled() &&
       !data_use_tracker_->ShouldUploadLogOnCellular(
           log_manager_.staged_log_hash().size())) {
     scheduler_->UploadCancelled();
+    upload_canceled = true;
   } else {
     SendStagedLog();
   }
+  UMA_HISTOGRAM_BOOLEAN("UMA.LogUpload.Canceled.CellularConstraint",

[Alexei Svitkine (slow), 2016/04/11 15:09:08]

Let's not log this unless IsUMACellularUploadLogicEnabled() is true, so that
we're not logging this when it's not relevant.

[gayane -on leave until 09-2017, 2016/04/11 15:40:46]

Done.

+                        upload_canceled);
 }
 
 bool MetricsService::ProvidersHaveInitialStabilityMetrics() {
   // Check whether any metrics provider has initial stability metrics.
   for (MetricsProvider* provider : metrics_providers_) {
     if (provider->HasInitialStabilityMetrics())
       return true;
   }
 
   return false;
@@ skipping 281 matching lines @@
                  base::Time::Now().ToTimeT());
 }
 
 void MetricsService::SkipAndDiscardUpload() {
   log_manager_.DiscardStagedLog();
   scheduler_->UploadCancelled();
   log_upload_in_progress_ = false;
 }
 
 }  // namespace metrics