content: convert zoom notifications to observer usage

content/content_browser.gypi

 # 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.
 
 {
   'dependencies': [
     'browser/speech/proto/speech_proto.gyp:speech_proto',
     '../base/base.gyp:base_static',
     '../crypto/crypto.gyp:crypto',
     '../google_apis/google_apis.gyp:google_apis',
@@ skipping 68 matching lines @@
     'public/browser/favicon_status.h',
     'public/browser/file_descriptor_info.h',
     'public/browser/font_list_async.h',
     'public/browser/geolocation.h',
     'public/browser/geolocation_permission_context.h',
     'public/browser/global_request_id.h',
     'public/browser/gpu_data_manager.h',
     'public/browser/gpu_data_manager_observer.h',
     'public/browser/histogram_fetcher.h',
     'public/browser/host_zoom_map.h',
+    'public/browser/host_zoom_map.cc',
     'public/browser/indexed_db_context.h',
     'public/browser/interstitial_page.h',
     'public/browser/invalidate_type.h',
     'public/browser/javascript_dialogs.h',
     'public/browser/keyboard_listener.h',
     'public/browser/load_from_memory_cache_details.cc',
     'public/browser/load_from_memory_cache_details.h',
     'public/browser/load_notification_details.h',
     'public/browser/media_devices_monitor.h',
     'public/browser/native_web_keyboard_event.h',
@@ skipping 1078 matching lines @@
         ['exclude', '^browser/speech/'],
       ],
     }],
     ['linux_use_libgps==1', {
       'dependencies': [
         '../build/linux/system.gyp:libgps',
       ],
     }],
   ],
 }