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

components/metrics/metrics_service.cc

Index: components/metrics/metrics_service.cc
diff --git a/components/metrics/metrics_service.cc b/components/metrics/metrics_service.cc
index 7e31ddb93156bf301ef333bd5cbe71bb7acc9691..e3b33c15c437c1620c467844c6fef3193f200daf 100644
--- a/components/metrics/metrics_service.cc
+++ b/components/metrics/metrics_service.cc
@@ -1155,11 +1155,19 @@ void MetricsService::RecordCurrentHistograms() {
 
 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() {