Separate page load metrics for backgrounded pages

components/page_load_metrics/browser/metrics_web_contents_observer.h

Index: components/page_load_metrics/browser/metrics_web_contents_observer.h
diff --git a/components/page_load_metrics/browser/metrics_web_contents_observer.h b/components/page_load_metrics/browser/metrics_web_contents_observer.h
index 5fa52c00a18fa2f0cc740c3c6770c23e21d0ca40..a0e2fdd64640e44ba3d9151ab0ea54b21aa4f3ef 100644
--- a/components/page_load_metrics/browser/metrics_web_contents_observer.h
+++ b/components/page_load_metrics/browser/metrics_web_contents_observer.h
@@ -5,6 +5,7 @@
 #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"
@@ -23,6 +24,33 @@ class Message;
 
 namespace page_load_metrics {
 
+class PageLoadTracker {
+ public:
+  PageLoadTracker(bool in_foreground);

[Bryan McQuade, 2015/09/29 00:32:19]

nit: single-arg constructor should be explicit

[Charlie Harrison, 2015/09/29 14:13:07]

Done.

+  ~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::Time background_time_;

[Bryan McQuade, 2015/09/29 00:32:19]

let's use a TimeTicks here, just to be clear that we really prefer to operate in
terms of monotonic clocks. We can convert to base::Time as we need to in the
code, but let's have our members using monotonic times as much as possible.
Eventually it'd be nice if we could convert navigation_start to a monotonic time
as well, but that's a bigger change that spans from blink back to browser
process, so can get to it later.

[Charlie Harrison, 2015/09/29 14:13:07]

Done.

+
+  PageLoadTiming timing_;
+
+  DISALLOW_COPY_AND_ASSIGN(PageLoadTracker);
+};
+
 // MetricsWebContentsObserver logs page load UMA metrics based on
 // IPC messages received from a MetricsRenderFrameObserver.
 class MetricsWebContentsObserver
@@ -36,7 +64,11 @@ class MetricsWebContentsObserver
                          content::RenderFrameHost* render_frame_host) override;
   void DidFinishNavigation(
       content::NavigationHandle* navigation_handle) override;
-  void RenderProcessGone(base::TerminationStatus status) override;
+  void DidStartNavigation(

[Bryan McQuade, 2015/09/29 00:32:19]

let's move DidStartNavigation's decl above DidFinishNavigation.

[Charlie Harrison, 2015/09/29 14:13:07]

Done.

+      content::NavigationHandle* navigation_handle) override;
+
+  void WasShown() override;
+  void WasHidden() override;
 
  private:
   explicit MetricsWebContentsObserver(content::WebContents* web_contents);
@@ -44,13 +76,19 @@ class 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);
 };