Add MetricsProvider::OnAppEnterBackground callback.

components/metrics/metrics_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_provider.h"
 
 namespace metrics {
 
 MetricsProvider::MetricsProvider() {
 }
 
 MetricsProvider::~MetricsProvider() {
 }
 
 void MetricsProvider::Init() {
 }
 
 void MetricsProvider::OnDidCreateMetricsLog() {
 }
 
 void MetricsProvider::OnRecordingEnabled() {
 }
 
 void MetricsProvider::OnRecordingDisabled() {
 }
 
+void MetricsProvider::OnAppEnterBackground() {
+}
+
 void MetricsProvider::ProvideSystemProfileMetrics(
     SystemProfileProto* system_profile_proto) {
 }
 
 bool MetricsProvider::HasInitialStabilityMetrics() {
   return false;
 }
 
 void MetricsProvider::ProvideInitialStabilityMetrics(
     SystemProfileProto* system_profile_proto) {
@@ skipping 15 matching lines @@
 
 void MetricsProvider::RecordHistogramSnapshots(
     base::HistogramSnapshotManager* snapshot_manager) {
 }
 
 void MetricsProvider::RecordInitialHistogramSnapshots(
     base::HistogramSnapshotManager* snapshot_manager) {
 }
 
 }  // namespace metrics