Make PrerenderHandle an observer of PrerenderContents.

chrome/browser/prerender/prerender_contents.h

Index: chrome/browser/prerender/prerender_contents.h
diff --git a/chrome/browser/prerender/prerender_contents.h b/chrome/browser/prerender/prerender_contents.h
index b41e02c4a27bc67a930e9d62de1c5cf4384679c8..6d04f733dfcf02a501e25eb42bb694222496f7b7 100644
--- a/chrome/browser/prerender/prerender_contents.h
+++ b/chrome/browser/prerender/prerender_contents.h
@@ -79,6 +79,10 @@ class PrerenderContents : public content::NotificationObserver,
     // Signals that the prerender has stopped running.
     virtual void OnPrerenderStop(PrerenderContents* contents) = 0;
 
+    // Signals the discovery, through redirects, of a new alias for this
+    // prerender.
+    virtual void OnPrerenderAddAlias(PrerenderContents* contents,
+                                     const GURL& alias_url);
    protected:
     Observer();
     virtual ~Observer() = 0;
@@ -129,8 +133,10 @@ class PrerenderContents : public content::NotificationObserver,
   virtual ~PrerenderContents();
 
   // All observers of a PrerenderContents are removed after the OnPrerenderStop
-  // event is sent, so there is no need for a RemoveObserver() method.
+  // event is sent, so there is no need to call RemoveObserver() in the normal
+  // use case.
   void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
 
   // For MatchComplete correctness, create a dummy replacement prerender
   // contents to stand in for this prerender contents that (which we are about
@@ -282,6 +288,7 @@ class PrerenderContents : public content::NotificationObserver,
   // These call out to methods on our Observers, using our observer_list_.
   void NotifyPrerenderStart();
   void NotifyPrerenderStop();
+  void NotifyPrerenderAddAlias(const GURL& alias_url);
 
   // Called whenever a RenderViewHost is created for prerendering.  Only called
   // once the RenderViewHost has a RenderView and RenderWidgetHostView.