content: convert zoom notifications to observer usage

content/public/browser/notification_types.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_NOTIFICATION_TYPES_H_
 #define CONTENT_PUBLIC_BROWSER_NOTIFICATION_TYPES_H_
 
 // This file describes various types used to describe and filter notifications
 // that pass through the NotificationService.
 //
@@ skipping 318 matching lines @@
   // register for AllSources() to receive this notification.  The details are
   // in a Details<ChildProcessData>.
   NOTIFICATION_CHILD_INSTANCE_CREATED,
 
   // Miscellaneous -------------------------------------------------------------
 
   // Sent before the repost form warning is brought up.
   // The source is a NavigationController.
   NOTIFICATION_REPOST_WARNING_SHOWN,
 
-  // Sent when the zoom level changes. The source is the HostZoomMap.  The
-  // details is a string of the hostname for which the zoom changed.  In case
-  // of a temporary zoom level change, the details is an empty string.
-  NOTIFICATION_ZOOM_LEVEL_CHANGED,
-
   // Custom notifications used by the embedder should start from here.
   NOTIFICATION_CONTENT_END,
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_NOTIFICATION_TYPES_H_