Record first layout time UMA metric in PageLoadHistograms.

chrome/renderer/page_load_histograms.h

 // Copyright (c) 2012 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_HISTOGRAMS_H_
 #define CHROME_RENDERER_PAGE_LOAD_HISTOGRAMS_H_
 
 #include "base/basictypes.h"
+#include "base/memory/weak_ptr.h"
 #include "content/public/renderer/render_view_observer.h"
 
 namespace blink {
 class WebDataSource;
 }
 
 namespace content {
 class DocumentState;
 }
 
 class PageLoadHistograms : public content::RenderViewObserver {
  public:
   explicit PageLoadHistograms(content::RenderView* render_view);
+  ~PageLoadHistograms() override;
 
  private:
   // RenderViewObserver implementation.
   void FrameWillClose(blink::WebFrame* frame) override;
   void ClosePage() override;
+  void DidUpdateLayout() override;
 
   // Dump all page load histograms appropriate for the given frame.
   //
   // This method will only dump once-per-instance, so it is safe to call
   // multiple times.
   //
   // The time points we keep are
   //    request: time document was requested by user
   //    start: time load of document started
   //    commit: time load of document started
   //    finish_document: main document loaded, before onload()
   //    finish_all_loads: after onload() and all resources are loaded
   //    first_paint: first paint performed
   //    first_paint_after_load: first paint performed after load is finished
   //    begin: request if it was user requested, start otherwise
   //
   // It's possible for the request time not to be set, if a client
   // redirect had been done (the user never requested the page)
   // Also, it's possible to load a page without ever laying it out
   // so first_paint and first_paint_after_load can be 0.
   void Dump(blink::WebFrame* frame);
 
+  bool ShouldDump(blink::WebFrame* frame);
+  void MaybeDumpFirstLayoutHistograms();
   void LogPageLoadTime(const content::DocumentState* load_times,
                        const blink::WebDataSource* ds) const;
 
+  bool dumped_first_layout_histograms_;
+  base::WeakPtrFactory<PageLoadHistograms> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(PageLoadHistograms);
 };
 
 #endif  // CHROME_RENDERER_PAGE_LOAD_HISTOGRAMS_H_