Merge subprocess metrics into global StatisticsRecorder.

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 6e89b26625a5ee263142206e4b7903dab52ea5d4..6a690f5251c893f7853e4f466cff590e611b011f 100644
--- a/components/metrics/metrics_provider.h
+++ b/components/metrics/metrics_provider.h
@@ -70,6 +70,10 @@ class MetricsProvider {
   virtual void ProvideGeneralMetrics(
       ChromeUserMetricsExtension* uma_proto);
 
+  // Called during regular collection to explicitly merge histogram deltas
+  // to the global StatisticsRecorder.
+  virtual void MergeHistogramDeltas();
+
   // 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(),