Separate page load metrics for backgrounded pages

components/page_load_metrics/browser/metrics_web_contents_observer.h

 // 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.
 
 #ifndef COMPONENTS_PAGE_LOAD_METRICS_BROWSER_PAGE_LOAD_METRICS_WEB_CONTENTS_OBSERVER_H_
 #define COMPONENTS_PAGE_LOAD_METRICS_BROWSER_PAGE_LOAD_METRICS_WEB_CONTENTS_OBSERVER_H_
 
+#include "base/containers/scoped_ptr_map.h"
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "components/page_load_metrics/common/page_load_timing.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 
 namespace content {
+

[Alexei Svitkine (slow), 2015/09/28 21:40:35]

Nit: I don't think it's convention to add empty lines around namespaces for fwd
declarations.

 class NavigationHandle;
 class RenderFrameHost;
+
 }  // namespace content
 
 namespace IPC {
+
 class Message;
+
 }  // namespace IPC
 
 namespace page_load_metrics {
 
+class PageLoadTracker {
+ public:
+  PageLoadTracker(bool in_foreground);
+  ~PageLoadTracker();
+  void Commit();
+  void WebContentsHidden();
+
+  // Returns true if the timing was successfully updated.
+  bool UpdateTiming(const PageLoadTiming& timing);
+
+ private:
+  void RecordTimingHistograms();
+
+  bool has_commit_;
+
+  // Initialize |background_time| to TimeDelta::Max() so that we can see if an
+  // event happened before a background by a simple < comparison. This will work
+  // even if the page was never backgrounded. We record separate metrics for
+  // any web contents that have been backgrounded, because metrics like
+  // layout/paint are delayed artificially when they occur in the bacground.
+  base::TimeDelta background_time;

[Alexei Svitkine (slow), 2015/09/28 21:40:35]

Nit: _

+
+  PageLoadTiming timing_;
+
+  DISALLOW_COPY_AND_ASSIGN(PageLoadTracker);
+};
+
 // MetricsWebContentsObserver logs page load UMA metrics based on
 // IPC messages received from a MetricsRenderFrameObserver.
 class MetricsWebContentsObserver
     : public content::WebContentsObserver,
       public content::WebContentsUserData<MetricsWebContentsObserver> {
  public:
   ~MetricsWebContentsObserver() override;
 
   // content::WebContentsObserver implementation:
   bool OnMessageReceived(const IPC::Message& message,
                          content::RenderFrameHost* render_frame_host) override;
   void DidFinishNavigation(
       content::NavigationHandle* navigation_handle) override;
-  void RenderProcessGone(base::TerminationStatus status) override;
+  void DidStartNavigation(
+      content::NavigationHandle* navigation_handle) override;
+
+  void WasShown() override;
+  void WasHidden() override;
 
  private:
   explicit MetricsWebContentsObserver(content::WebContents* web_contents);
   friend class content::WebContentsUserData<MetricsWebContentsObserver>;
   friend class MetricsWebContentsObserverTest;
 
   void OnTimingUpdated(content::RenderFrameHost*, const PageLoadTiming& timing);
-  void RecordTimingHistograms();
 
   bool IsRelevantNavigation(content::NavigationHandle* navigation_handle);
 
-  // Will be null before any navigations have committed. When a navigation
-  // commits we will initialize this as empty.
-  scoped_ptr<PageLoadTiming> current_timing_;
+  // True if the web contents is currently in the foreground.
+  bool in_foreground_;
+
+  // This map tracks all of the navigations ongoing that are not committed
+  // yet. Once a navigation is committed, it moves from the map to
+  // committed_load_. Note that a PageLoadTrackers NavigationHandle is only
+  // valid until commit time, when we remove it from the map.
+  base::ScopedPtrMap<content::NavigationHandle*, scoped_ptr<PageLoadTracker>>
+      provisional_loads_;
+  scoped_ptr<PageLoadTracker> committed_load_;
 
   DISALLOW_COPY_AND_ASSIGN(MetricsWebContentsObserver);
 };
 
 }  // namespace page_load_metrics
 
 #endif  // COMPONENTS_PAGE_LOAD_METRICS_BROWSER_PAGE_LOAD_METRICS_WEB_CONTENTS_OBSERVER_H_