Introduce a MetricsDataProvider interface.

components/metrics/metrics_provider.h

Index: components/metrics/metrics_provider.h
===================================================================
--- components/metrics/metrics_provider.h	(revision 0)
+++ components/metrics/metrics_provider.h	(working copy)
@@ -0,0 +1,50 @@
+// 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 {
+
+class ChromeUserMetricsExtension;
+class SystemProfileProto;
+class SystemProfileProto_Stability;
+
+// MetricsProvider is an interface allowing different parts of the UMA protos to
+// be filled out by different classes.
+class MetricsProvider {
+ public:
+  MetricsProvider() {}
+  virtual ~MetricsProvider() {}
+
+  // Called when metrics recording has been enabled.
+  virtual void OnRecordingEnabled() {}
+
+  // Called when metrics recording has been disabled.
+  virtual void OnRecordingDisabled() {}
+
+  // Provides additional metrics into the system profile.
+  virtual void ProvideSystemProfileMetrics(
+      SystemProfileProto* system_profile_proto) {}
+
+  // Provides additional stability metrics. Stability metrics can be provided
+  // directly into |stability_proto| fields or by logging stability histograms
+  // via the UMA_STABILITY_HISTOGRAM_ENUMERATION() macro.
+  virtual void ProvideStabilityMetrics(
+      SystemProfileProto_Stability* stability_proto) {}
+
+  // Provides general metrics that are neither system profile nor stability
+  // metrics.
+  virtual void ProvideGeneralMetrics(
+      ChromeUserMetricsExtension* uma_proto) {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MetricsProvider);
+};
+
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_METRICS_PROVIDER_H_