Support saving browser metrics to disk and reading them during next run.

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 1137 matching lines @@
     if ((*it)->flags() & base::Histogram::kUmaTargetedHistogramFlag)
       histogram_snapshot_manager_.PrepareDelta(*it);
   }
   for (MetricsProvider* provider : metrics_providers_)
     provider->RecordHistogramSnapshots(&histogram_snapshot_manager_);
   histogram_snapshot_manager_.FinishDeltas();
 }
 
 void MetricsService::RecordCurrentStabilityHistograms() {
   DCHECK(log_manager_.current_log());
+  histogram_snapshot_manager_.StartDeltas();
   // "true" indicates that StatisticsRecorder should include histograms in
   // persistent storage.
-  histogram_snapshot_manager_.PrepareDeltas(
-      base::StatisticsRecorder::begin(true), base::StatisticsRecorder::end(),
-      base::Histogram::kNoFlags, base::Histogram::kUmaStabilityHistogramFlag);
+  auto end = base::StatisticsRecorder::end();
+  for (auto it = base::StatisticsRecorder::begin(true); it != end; ++it) {
+    if (((*it)->flags() & base::Histogram::kUmaStabilityHistogramFlag) ==
+        base::Histogram::kUmaStabilityHistogramFlag) {
+      histogram_snapshot_manager_.PrepareDelta(*it);
+    }
+  }
+  for (MetricsProvider* provider : metrics_providers_)
+    provider->RecordStabilityHistogramSnapshots(&histogram_snapshot_manager_);

[Ilya Sherman, 2016/05/04 06:48:08]

This doesn't seem like the right place to add this code.  You're interested in
just recording these histograms for the initial log, right?

I think it might be worthwhile to split this CL back into two parts, with the
first CL just for saving the metrics, and the second for actually uploading
them.  That way, you can land the first part while we figure out the details for
the second part.

[bcwhite, 2016/05/04 14:12:51]

Correct.  This method is called only from PrepareInitialStabilityLog().
I could but there's nothing waiting on the (small) part that writes the file
other than a small change to setup.exe to call it rather than do the same thing
in its own code.

+  histogram_snapshot_manager_.FinishDeltas();
 }
 
 void MetricsService::LogCleanShutdown() {
   // Redundant setting to assure that we always reset this value at shutdown
   // (and that we don't use some alternate path, and not call LogCleanShutdown).
   clean_shutdown_status_ = CLEANLY_SHUTDOWN;
 
   clean_exit_beacon_.WriteBeaconValue(true);
   RecordCurrentState(local_state_);
   local_state_->SetInteger(prefs::kStabilityExecutionPhase,
@@ skipping 18 matching lines @@
                  base::Time::Now().ToTimeT());
 }
 
 void MetricsService::SkipAndDiscardUpload() {
   log_manager_.DiscardStagedLog();
   scheduler_->UploadCancelled();
   log_upload_in_progress_ = false;
 }
 
 }  // namespace metrics