Add PLMObserver::FlushMetricsOnAppEnterBackground.

chrome/browser/page_load_metrics/metrics_web_contents_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/metrics_web_contents_observer.h"
 
 #include <algorithm>
 #include <ostream>
 #include <string>
 #include <utility>
@@ skipping 455 matching lines @@
   for (const auto& observer : observers_) {
     observer->OnUserInput(event);
   }
 }
 
 void PageLoadTracker::FlushMetricsOnAppEnterBackground() {
   if (!app_entered_background_) {
     RecordAppBackgroundPageLoadCompleted(false);
     app_entered_background_ = true;
   }
+
+  const PageLoadExtraInfo info = ComputePageLoadExtraInfo();
+  for (auto it = observers_.begin(); it != observers_.end();) {
+    if ((*it)->FlushMetricsOnAppEnterBackground(timing_, info) ==
+        PageLoadMetricsObserver::STOP_OBSERVING) {
+      it = observers_.erase(it);
+    } else {
+      ++it;
+    }
+  }
 }
 
 void PageLoadTracker::NotifyClientRedirectTo(
     const PageLoadTracker& destination) {
   if (timing_.first_paint) {
     base::TimeTicks first_paint_time =
         navigation_start() + timing_.first_paint.value();
     base::TimeDelta first_paint_to_navigation;
     if (destination.navigation_start() > first_paint_time)
       first_paint_to_navigation =
@@ skipping 422 matching lines @@
     const blink::WebInputEvent& event) {
   // Ignore browser navigation or reload which comes with type Undefined.
   if (event.type == blink::WebInputEvent::Type::Undefined)
     return;
 
   if (committed_load_)
     committed_load_->OnInputEvent(event);
 }
 
 void MetricsWebContentsObserver::FlushMetricsOnAppEnterBackground() {
+  // Signal to observers that we've been backgrounded, in cases where the
+  // FlushMetricsOnAppEnterBackground callback gets invoked before the
+  // associated WasHidden callback.
+  WasHidden();
+
   if (committed_load_)
     committed_load_->FlushMetricsOnAppEnterBackground();
   for (const auto& kv : provisional_loads_) {
     kv.second->FlushMetricsOnAppEnterBackground();
   }
   for (const auto& tracker : aborted_provisional_loads_) {
     tracker->FlushMetricsOnAppEnterBackground();
   }
 }
 
@@ skipping 145 matching lines @@
     content::NavigationHandle* navigation_handle) const {
   DCHECK(navigation_handle->IsInMainFrame());
   DCHECK(!navigation_handle->HasCommitted() ||
          !navigation_handle->IsSamePage());
 
   return BrowserPageTrackDecider(embedder_interface_.get(), web_contents(),
                                  navigation_handle).ShouldTrack();
 }
 
 }  // namespace page_load_metrics