Reapply and fix r73019. BalloonViewImpl has a different implemementation on

chrome/browser/notifications/balloon_collection.h

Index: chrome/browser/notifications/balloon_collection.h
diff --git a/chrome/browser/notifications/balloon_collection.h b/chrome/browser/notifications/balloon_collection.h
index 690975937dbd8eacbb93eca6d62a5a12db892f75..4cae9095d9186641820ee4ecf63b11962d08d33b 100644
--- a/chrome/browser/notifications/balloon_collection.h
+++ b/chrome/browser/notifications/balloon_collection.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -48,11 +48,9 @@ class BalloonCollection {
 
   static BalloonCollection* Create();
 
-  BalloonCollection()
-      : space_change_listener_(NULL) {
-  }
+  BalloonCollection();
 
-  virtual ~BalloonCollection() {}
+  virtual ~BalloonCollection();
 
   // Adds a new balloon for the specified notification.
   virtual void Add(const Notification& notification,