content: convert zoom notifications to observer usage

content/public/browser/host_zoom_map.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_PUBLIC_BROWSER_HOST_ZOOM_MAP_H_
 #define CONTENT_PUBLIC_BROWSER_HOST_ZOOM_MAP_H_
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "content/common/content_export.h"
 
 namespace content {
 
 class BrowserContext;
+class HostZoomMapImpl;
 class ResourceContext;
 
 // Maps hostnames to custom zoom levels.  Written on the UI thread and read on
 // any thread.  One instance per browser context. Must be created on the UI
 // thread, and it'll delete itself on the UI thread as well.
 class HostZoomMap {
  public:
   CONTENT_EXPORT static HostZoomMap* GetForBrowserContext(
       BrowserContext* browser_context);
 
+  class Observer {

[jam, 2013/01/24 01:28:35]

nit: per c++ style guide, and convention, prefer to put every class into a
separate file. this avoids having to include this header in other headers that
just want to implement the interface (so this would be host_zoom_map_observer.h,
and the class would be HostZoomMapObserver)

[Paweł Hajdan Jr., 2013/01/24 19:42:38]

Done.

+   public:
+    Observer();
+    explicit Observer(HostZoomMap* map);
+    virtual ~Observer();
+
+    // Called when the zoom level changes. |host| is a string of the hostname
+    // for which the zoom changed (empty string for temporary changes).
+    virtual void OnZoomLevelChanged(const std::string& host) = 0;
+
+   protected:
+    void Observe(HostZoomMap* map);
+
+   private:
+    friend class HostZoomMapImpl;
+
+    void HostZoomMapImplDestroyed();
+
+    HostZoomMapImpl* host_zoom_map_;
+
+    DISALLOW_COPY_AND_ASSIGN(Observer);
+  };
+
   // Copy the zoom levels from the given map. Can only be called on the UI
   // thread.
   virtual void CopyFrom(HostZoomMap* copy) = 0;
 
   // Returns the zoom level for the host or spec for a given url. The zoom
   // level is determined by the host portion of the URL, or (in the absence of
   // a host) the complete spec of the URL. In most cases, there is no custom
   // zoom level, and this returns the user's default zoom level.  Otherwise,
   // returns the saved zoom level, which may be positive (to zoom in) or
   // negative (to zoom out).
@@ skipping 12 matching lines @@
   virtual double GetDefaultZoomLevel() const = 0;
   virtual void SetDefaultZoomLevel(double level) = 0;;
 
  protected:
   virtual ~HostZoomMap() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_HOST_ZOOM_MAP_H_