Fix PPLT metric for the new TabContents based prerendering

chrome/browser/prerender/prerender_observer.h

 // Copyright (c) 2011 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_BROWSER_PRERENDER_PRERENDER_OBSERVER_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_OBSERVER_H_
 
 #include "content/browser/tab_contents/tab_contents_observer.h"
 
 #include "base/time.h"
@@ skipping 18 matching lines @@
                                                bool has_opener_set) OVERRIDE;
   virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
   virtual void DidStopLoading() OVERRIDE;
 
   // Message handler.
   void OnDidStartProvisionalLoadForFrame(int64 frame_id,
                                          bool main_frame,
                                          bool has_opener_set,
                                          const GURL& url);
 
+  // Called when this prerendered TabContents has just been swapped in.
+  void PrerenderSwappedIn();
+
  private:
   // Retrieves the PrerenderManager, or NULL, if none was found.
   PrerenderManager* MaybeGetPrerenderManager();
 
   // Checks with the PrerenderManager if the specified URL has been preloaded,
   // and if so, swap the RenderViewHost with the preload into this TabContents
   // object.
   bool MaybeUsePreloadedPage(const GURL& url, bool has_opener_set);
 
   // Returns whether the TabContents being observed is currently prerendering.
   bool IsPrerendering();
 
   // System time at which the current load was started for the purpose of
   // the perceived page load time (PPLT).
   base::TimeTicks pplt_load_start_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderObserver);
 };
 
 }  // namespace prerender
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_OBSERVER_H_