Record document mode histogram in UMA on every upload.

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/basictypes.h"
 
 namespace metrics {
@@ skipping 30 matching lines @@
   // directly into |stability_proto| fields or by logging stability histograms
   // via the UMA_STABILITY_HISTOGRAM_ENUMERATION() macro.
   virtual void ProvideStabilityMetrics(
       SystemProfileProto* system_profile_proto);
 
   // 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.
+  // metrics. May also be used to add histograms when final metrics are
+  // collected right before upload.
   virtual void ProvideGeneralMetrics(
       ChromeUserMetricsExtension* uma_proto);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MetricsProvider);
 };
 
 }  // namespace metrics
 
 #endif  // COMPONENTS_METRICS_METRICS_PROVIDER_H_