Notify page load metrics when the app enters the background.

chrome/browser/page_load_metrics/metrics_web_contents_observer.h

Index: chrome/browser/page_load_metrics/metrics_web_contents_observer.h
diff --git a/chrome/browser/page_load_metrics/metrics_web_contents_observer.h b/chrome/browser/page_load_metrics/metrics_web_contents_observer.h
index 5b072f75d776cf392e66c0bb3bfeded269f4f222..b53fb5771efd11e44b06b1ac1e82862383d620d7 100644
--- a/chrome/browser/page_load_metrics/metrics_web_contents_observer.h
+++ b/chrome/browser/page_load_metrics/metrics_web_contents_observer.h
@@ -41,6 +41,7 @@ extern const char kAbortChainSizeForwardBack[];
 extern const char kAbortChainSizeNewNavigation[];
 extern const char kAbortChainSizeNoCommit[];
 extern const char kAbortChainSizeSameURL[];
+extern const char kPageLoadCompletedAfterAppBackground[];
 
 }  // namespace internal
 
@@ -143,6 +144,12 @@ class PageLoadTracker {
 
   void OnInputEvent(const blink::WebInputEvent& event);
 
+  // Flush any buffered metrics, as part of the metrics subsystem persisting
+  // metrics as the application goes into the background. The application may be
+  // killed at any time after this method is invoked without further
+  // notification.
+  void FlushMetricsOnAppEnterBackground();
+
   void NotifyClientRedirectTo(const PageLoadTracker& destination);
 
   // Returns true if the timing was successfully updated.
@@ -220,6 +227,10 @@ class PageLoadTracker {
   // metrics in DidFinishNavigation.
   bool did_stop_tracking_;
 
+  // Whether the application went into the background when this PageLoadTracker
+  // was active. This is a temporary boolean for UMA tracking.
+  bool app_entered_background_;
+
   // The navigation start in TimeTicks, not the wall time reported by Blink.
   const base::TimeTicks navigation_start_;
 
@@ -302,6 +313,12 @@ class MetricsWebContentsObserver
   void RenderViewHostChanged(content::RenderViewHost* old_host,
                              content::RenderViewHost* new_host) override;
 
+  // Flush any buffered metrics, as part of the metrics subsystem persisting
+  // metrics as the application goes into the background. The application may be
+  // killed at any time after this method is invoked without further
+  // notification.
+  void FlushMetricsOnAppEnterBackground();
+
   // This getter function is required for testing.
   const PageLoadExtraInfo GetPageLoadExtraInfoForCommittedLoad();