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

components/metrics/metrics_provider.h

Index: components/metrics/metrics_provider.h
diff --git a/components/metrics/metrics_provider.h b/components/metrics/metrics_provider.h
index 664e5dbc539299c9e9682378901e558ff723aa81..6e89b26625a5ee263142206e4b7903dab52ea5d4 100644
--- a/components/metrics/metrics_provider.h
+++ b/components/metrics/metrics_provider.h
@@ -70,13 +70,20 @@ class MetricsProvider {
   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 initial metrics 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 RecordInitialHistogramSnapshots(
+      base::HistogramSnapshotManager* snapshot_manager);
+
  private:
   DISALLOW_COPY_AND_ASSIGN(MetricsProvider);
 };