Add PLMObserver::FlushMetricsOnAppEnterBackground.

chrome/browser/page_load_metrics/page_load_metrics_observer.cc

 // Copyright 2015 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 "chrome/browser/page_load_metrics/page_load_metrics_observer.h"
 
 namespace page_load_metrics {
 
 PageLoadExtraInfo::PageLoadExtraInfo(
     const base::Optional<base::TimeDelta>& first_background_time,
@@ skipping 26 matching lines @@
 PageLoadExtraInfo::PageLoadExtraInfo(const PageLoadExtraInfo& other) = default;
 
 PageLoadExtraInfo::~PageLoadExtraInfo() {}
 
 FailedProvisionalLoadInfo::FailedProvisionalLoadInfo(base::TimeDelta interval,
                                                      net::Error error)
     : time_to_failed_provisional_load(interval), error(error) {}
 
 FailedProvisionalLoadInfo::~FailedProvisionalLoadInfo() {}
 
+PageLoadMetricsObserver::ObservePolicy
+PageLoadMetricsObserver::FlushMetricsOnAppEnterBackground(
+    const PageLoadTiming& timing,
+    const PageLoadExtraInfo& extra_info) {
+  return CONTINUE_OBSERVING;
+}
+
 }  // namespace page_load_metrics