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

components/metrics/metrics_provider.h

 // 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.
 
 #ifndef COMPONENTS_METRICS_METRICS_PROVIDER_H_
 #define COMPONENTS_METRICS_METRICS_PROVIDER_H_
 
 #include "base/macros.h"
 
 namespace base {
@@ skipping 52 matching lines @@
   // Called to indicate that saved stability prefs should be cleared, e.g.
   // because they are from an old version and should not be kept.
   virtual void ClearSavedStabilityMetrics();
 
   // Provides general metrics that are neither system profile nor stability
   // metrics. May also be used to add histograms when final metrics are
   // collected right before upload.
   virtual void ProvideGeneralMetrics(
       ChromeUserMetricsExtension* uma_proto);
 
-  // Called during collection to explicitly load histogram snapshots using a
-  // snapshot manager. PrepareDeltas() will have already been called and
-  // FinishDeltas() will be called later; calls to only PrepareDelta(), not
-  // PrepareDeltas (plural), should be made.
+  // Called during regular collection to explicitly load histogram snapshots
+  // using a snapshot manager. PrepareDeltas() will have already been called
+  // and FinishDeltas() will be called later; calls to only PrepareDelta(),
+  // not PrepareDeltas (plural), should be made.
   virtual void RecordHistogramSnapshots(
       base::HistogramSnapshotManager* snapshot_manager);
 
+  // Called during collection of "stability" metrics to explicitly load

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

It's not actually "stability" that's relevant her.  Rather, this hook is for the
initial metrics log, associated with the previous session, right?  I'd clarify
the method name to mention "initial" rather than "stability", and not mention
"stability" in the docs.

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

Done.

+  // histogram snapshots using a snapshot manager. PrepareDeltas() will have
+  // already been called and FinishDeltas() will be called later; calls to
+  // only PrepareDelta(), not PrepareDeltas (plural), should be made.
+  virtual void RecordStabilityHistogramSnapshots(
+      base::HistogramSnapshotManager* snapshot_manager);
+
  private:
   DISALLOW_COPY_AND_ASSIGN(MetricsProvider);
 };
 
 }  // namespace metrics
 
 #endif  // COMPONENTS_METRICS_METRICS_PROVIDER_H_