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 "base/callback.h"
 #include "content/common/content_export.h"
 
 namespace content {
 
 class BrowserContext;
+class HostZoomMapImpl;

[jam, 2013/01/30 17:50:44]

nit: not needed anymore

 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:
+  typedef base::Callback<void(const std::string&)> ZoomLevelChangedCallback;

[jam, 2013/01/30 17:50:44]

nit: the convention in the content api is to declare the callbacks right above
the method that uses them

please document what the string parameter in the callback is used for

+
   CONTENT_EXPORT static HostZoomMap* GetForBrowserContext(
       BrowserContext* browser_context);
 
   // 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).
   //
   // This may be called on any thread.
   virtual double GetZoomLevel(const std::string& host) const = 0;
 
   // Sets the zoom level for the host or spec for a given url to |level|.  If
   // the level matches the current default zoom level, the host is erased
   // from the saved preferences; otherwise the new value is written out.
   //
   // This should only be called on the UI thread.
   virtual void SetZoomLevel(const std::string& host, double level) = 0;
 
   // Get/Set the default zoom level for pages that don't override it.
   virtual double GetDefaultZoomLevel() const = 0;
   virtual void SetDefaultZoomLevel(double level) = 0;;
 
+  // Add and remove zoom level changed callbacks.
+  virtual void AddZoomLevelChangedCallback(
+      ZoomLevelChangedCallback callback) = 0;

[jam, 2013/01/30 17:50:44]

nit: callbacks, like other complex types, are passed as const references

+  virtual void RemoveZoomLevelChangedCallback(
+      ZoomLevelChangedCallback callback) = 0;
+
  protected:
   virtual ~HostZoomMap() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_HOST_ZOOM_MAP_H_