Introduce a MetricsDataProvider interface.

components/metrics/metrics_data_provider.cc

+// 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.
+
+#include "components/metrics/metrics_data_provider.h"
+
+namespace metrics {
+
+MetricsDataProvider::MetricsDataProvider() {
+}
+
+MetricsDataProvider::~MetricsDataProvider() {
+}
+
+void MetricsDataProvider::ProvideStabilityMetrics(
+    SystemProfileProto_Stability* stability_proto) {
+}
+
+void MetricsDataProvider::ProvideSystemProfileMetrics(
+    SystemProfileProto* system_profile_proto) {
+}
+
+void MetricsDataProvider::ProvideGeneralMetrics(
+    ChromeUserMetricsExtension* uma_proto) {
+}
+
+}  // namespace metrics

[Ilya Sherman, 2014/05/19 14:45:00]

nit: I'd inline the entire contents of this file.  If it's good enough for
WebContentsObserver, it's probably good enough for us :)

https://code.google.com/p/chromium/codesearch#chromium/src/content/public/bro...

(I just remembered that the content API does this pretty consistently
throughout.)

[Alexei Svitkine (slow), 2014/05/19 15:23:02]

Done.