Persist setup metrics and have Chrome report them during UMA upload.

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 c0571954688e60de0074692916763b18d4f510ba..664e5dbc539299c9e9682378901e558ff723aa81 100644
--- a/components/metrics/metrics_provider.h
+++ b/components/metrics/metrics_provider.h
@@ -7,6 +7,10 @@
 
 #include "base/macros.h"
 
+namespace base {
+class HistogramSnapshotManager;
+}  // namespace base
+
 namespace metrics {
 
 class ChromeUserMetricsExtension;
@@ -66,6 +70,13 @@ 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.
+  virtual void RecordHistogramSnapshots(
+      base::HistogramSnapshotManager* snapshot_manager);
+
  private:
   DISALLOW_COPY_AND_ASSIGN(MetricsProvider);
 };