Add support for tracking loading behavior of child frames.

chrome/renderer/page_load_metrics/metrics_render_frame_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 CHROME_RENDERER_PAGE_LOAD_METRICS_METRICS_RENDER_FRAME_OBSERVER_H_
 #define CHROME_RENDERER_PAGE_LOAD_METRICS_METRICS_RENDER_FRAME_OBSERVER_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "chrome/common/page_load_metrics/page_load_timing.h"
 #include "content/public/renderer/render_frame_observer.h"
 #include "third_party/WebKit/public/platform/WebLoadingBehaviorFlag.h"
 
 namespace base {
 class Timer;
 }  // namespace base
 
 namespace page_load_metrics {
 
 class PageTimingMetricsSender;
 
-// MetricsRenderFrameObserver observes RenderFrame notifications, and
-// sends page load timing information to the browser process over IPC.
+// MetricsRenderFrameObserver observes RenderFrame notifications, and sends page
+// load timing information to the browser process over IPC. A
+// MetricsRenderFrameObserver is instantiated for each frame (main frames and
+// child frames). MetricsRenderFrameObserver dispatches timing and metadata
+// updates for main frames, but only metadata updates for child frames.
 class MetricsRenderFrameObserver : public content::RenderFrameObserver {
  public:
   explicit MetricsRenderFrameObserver(content::RenderFrame* render_frame);
   ~MetricsRenderFrameObserver() override;
 
   // RenderFrameObserver implementation
   void DidChangePerformanceTiming() override;
   void DidObserveLoadingBehavior(
       blink::WebLoadingBehaviorFlag behavior) override;
   void DidCommitProvisionalLoad(bool is_new_navigation,
                                 bool is_same_page_navigation) override;
   void OnDestruct() override;
 
+  // Invoked when a frame is going away. This is our last chance to send IPCs
+  // before being destroyed.
+  void FrameDetached() override;
+
  private:
   // Will be null when we're not actively sending metrics.
   std::unique_ptr<PageTimingMetricsSender> page_timing_metrics_sender_;
 
   void SendMetrics();
   virtual bool ShouldSendMetrics() const;
   virtual PageLoadTiming GetTiming() const;
   virtual std::unique_ptr<base::Timer> CreateTimer() const;
   virtual bool HasNoRenderFrame() const;
+  virtual bool IsMainFrame() const;
 
   DISALLOW_COPY_AND_ASSIGN(MetricsRenderFrameObserver);
 };
 
 }  // namespace page_load_metrics
 
 #endif  // CHROME_RENDERER_PAGE_LOAD_METRICS_METRICS_RENDER_FRAME_OBSERVER_H_