content: convert zoom notifications to observer usage

content/browser/host_zoom_map_impl.h

 // Copyright (c) 2012 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 CONTENT_BROWSER_HOST_ZOOM_MAP_IMPL_H_
 #define CONTENT_BROWSER_HOST_ZOOM_MAP_IMPL_H_
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/compiler_specific.h"
+#include "base/observer_list.h"
 #include "base/sequenced_task_runner_helpers.h"
 #include "base/supports_user_data.h"
 #include "base/synchronization/lock.h"
 #include "content/public/browser/host_zoom_map.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 
 namespace content {
 
 // HostZoomMap needs to be deleted on the UI thread because it listens
@@ skipping 27 matching lines @@
   void SetTemporaryZoomLevel(int render_process_id,
                              int render_view_id,
                              double level);
 
   // NotificationObserver implementation.
   virtual void Observe(int type,
                        const NotificationSource& source,
                        const NotificationDetails& details) OVERRIDE;
 
  private:
+  friend class HostZoomMap::Observer;
+
   typedef std::map<std::string, double> HostZoomLevels;
 
+  // Add and remove observers. Adding or removing multiple times has no effect.
+  // The order in which notifications are sent to observers is undefined.
+  // Clients must be sure to remove the observer before they go away.
+  void AddObserver(HostZoomMap::Observer* observer);
+  void RemoveObserver(HostZoomMap::Observer* observer);
+
+  // A list of observers. Weak references.
+  ObserverList<HostZoomMap::Observer> observers_;
+
   // Copy of the pref data, so that we can read it on the IO thread.
   HostZoomLevels host_zoom_levels_;
   double default_zoom_level_;
 
   struct TemporaryZoomLevel {
     int render_process_id;
     int render_view_id;
     double zoom_level;
   };
 
   // Don't expect more than a couple of tabs that are using a temporary zoom
   // level, so vector is fine for now.
   std::vector<TemporaryZoomLevel> temporary_zoom_levels_;
 
   // Used around accesses to |host_zoom_levels_|, |default_zoom_level_| and
   // |temporary_zoom_levels_| to guarantee thread safety.
   mutable base::Lock lock_;
 
   NotificationRegistrar registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(HostZoomMapImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_HOST_ZOOM_MAP_IMPL_H_