Record first layout time UMA metric in PageLoadHistograms.

chrome/renderer/page_load_histograms.h

Index: chrome/renderer/page_load_histograms.h
diff --git a/chrome/renderer/page_load_histograms.h b/chrome/renderer/page_load_histograms.h
index 5eed9bbee814666e3fda0fe8170430f54d58ee56..39f8cc5a9cb8c75d3d70b7dbaa4f5d0c9c38cfc2 100644
--- a/chrome/renderer/page_load_histograms.h
+++ b/chrome/renderer/page_load_histograms.h
@@ -6,6 +6,7 @@
 #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 {
@@ -19,11 +20,13 @@ 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.
   //
@@ -46,9 +49,14 @@ class PageLoadHistograms : public content::RenderViewObserver {
   // 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);
 };