Make PrerenderHandle an observer of PrerenderContents.

chrome/browser/prerender/prerender_handle.h

Index: chrome/browser/prerender/prerender_handle.h
diff --git a/chrome/browser/prerender/prerender_handle.h b/chrome/browser/prerender/prerender_handle.h
index 90a9dcc3f1eb0dd4e2e4a35676d2512f4ccc359b..e0735823465064b25a6c3c656e39ca3bbaca45a7 100644
--- a/chrome/browser/prerender/prerender_handle.h
+++ b/chrome/browser/prerender/prerender_handle.h
@@ -7,6 +7,7 @@
 
 #include "base/basictypes.h"
 #include "base/memory/weak_ptr.h"
+#include "base/observer_list.h"
 #include "base/threading/non_thread_safe.h"
 #include "chrome/browser/prerender/prerender_manager.h"
 
@@ -23,14 +24,36 @@ class PrerenderContents;
 // A class representing a running prerender to a client of the PrerenderManager.
 // Methods on PrerenderManager which start prerenders return a caller-owned
 // PrerenderHandle* to the client (or NULL if they are unable to start a
-// prerender). Because the PrerenderManager can stop running prerenders at any
-// time, callers may wish to check PrerenderHandle::IsValid() before operating
-// on their prerenders.
-class PrerenderHandle : public base::NonThreadSafe {
+// prerender). The PrerenderManager can stop running prerenders at any time,
+// which will make calls on the handle into no-ops.

[mmenke, 2012/12/11 19:53:45]

They're also no-ops if the prerender has not yet started, in which case we use
the destruction of the handle itself as a signal not to start prerendering.

[gavinp, 2012/12/13 13:38:03]

Done.

+class PrerenderHandle : public base::NonThreadSafe,
+                        public PrerenderContents::Observer {
  public:
+  class Observer {
+   public:
+    virtual ~Observer();
+
+    // Signals that the prerender has started running.
+    virtual void OnPrerenderStart(PrerenderHandle* handle) = 0;
+
+    // Signals that the prerender has stopped running.
+    virtual void OnPrerenderStop(PrerenderHandle* handle) = 0;
+
+    // Signals the discovery, through redirects, of a new alias for this
+    // prerender.
+    virtual void OnPrerenderAddAlias(PrerenderHandle* handle,
+                                     const GURL& alias_url) = 0;
+
+   protected:
+    Observer();
+  };
+
   // Before calling the destructor, the caller must invalidate the handle by
   // calling either OnNavigateAway or OnCancel.
-  ~PrerenderHandle();
+  virtual ~PrerenderHandle();
+
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
 
   // The launcher is navigating away from the context that launched this
   // prerender. The prerender will likely stay alive briefly though, in case we
@@ -45,15 +68,10 @@ class PrerenderHandle : public base::NonThreadSafe {
   // nothing.
   void OnCancel();
 
-  // True if the prerender handle is still connected to a (pending or running)
-  // prerender. Handles can become invalid through explicit requests by the
-  // client, such as calling OnCancel() or OnNavigateAway(), and handles
-  // also become invalid when the PrerenderManager cancels prerenders.
-  bool IsValid() const;
-
-  // True if this prerender was launched by a page that was itself being
-  // prerendered, and so has not yet been started.
-  bool IsPending() const;
+  // True if this prerender handle has been canceled.
+  bool has_been_canceled() const {
+    return has_been_canceled_;
+  }
 
   // True if this prerender is currently active.
   bool IsPrerendering() const;
@@ -66,8 +84,19 @@ class PrerenderHandle : public base::NonThreadSafe {
 
   explicit PrerenderHandle(PrerenderManager::PrerenderData* prerender_data);
 
-  void SwapPrerenderDataWith(PrerenderHandle* other_prerender_handle);
+  void AdoptPrerenderDataFrom(PrerenderHandle* other_handle);
+
+  // From PrerenderContents::Observer:
+  virtual void OnPrerenderStart(PrerenderContents* prerender_contents) OVERRIDE;
+  virtual void OnPrerenderStop(PrerenderContents* prerender_contents) OVERRIDE;
+  virtual void OnPrerenderAddAlias(PrerenderContents* prerender_contents,
+                                   const GURL& alias_url) OVERRIDE;
+  virtual void OnPrerenderCreatedMatchCompleteReplacement(
+      PrerenderContents* contents, PrerenderContents* replacement) OVERRIDE;
+
+  ObserverList<Observer> observer_list_;

[mmenke, 2012/12/12 16:54:12]

Do we really need an observer list?  Seems like in general, we're going to have
at most one Observer - the owner.

[gavinp, 2012/12/13 13:38:03]

We can do away with the list. Done.

 
+  bool has_been_canceled_;
   base::WeakPtr<PrerenderManager::PrerenderData> prerender_data_;
   base::WeakPtrFactory<PrerenderHandle> weak_ptr_factory_;