chromeos: Remove UpdateObserver, which has been unused for long.

chrome/chrome_browser.gypi

 # Copyright (c) 2011 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.
 
 {
   'targets': [
     {
       'target_name': 'browser',
       'type': 'static_library',
       'dependencies': [
@@ skipping 776 matching lines @@
         'browser/chromeos/system/touchpad_settings.cc',
         'browser/chromeos/system/touchpad_settings.h',
         'browser/chromeos/system/udev_info_provider.cc',
         'browser/chromeos/system/udev_info_provider.h',
         'browser/chromeos/system_key_event_listener.cc',
         'browser/chromeos/system_key_event_listener.h',
         'browser/chromeos/tab_closeable_state_watcher.cc',
         'browser/chromeos/tab_closeable_state_watcher.h',
         'browser/chromeos/tab_first_render_watcher.cc',
         'browser/chromeos/tab_first_render_watcher.h',
-        'browser/chromeos/update_observer.cc',
-        'browser/chromeos/update_observer.h',
         'browser/chromeos/upgrade_detector_chromeos.cc',
         'browser/chromeos/upgrade_detector_chromeos.h',
         'browser/chromeos/user_cros_settings_provider.cc',
         'browser/chromeos/user_cros_settings_provider.h',
         'browser/chromeos/version_loader.cc',
         'browser/chromeos/version_loader.h',
         'browser/chromeos/view_ids.h',
         'browser/chromeos/views/copy_background.cc',
         'browser/chromeos/views/copy_background.h',
         'browser/chromeos/views/dropdown_button.cc',
@@ skipping 4376 matching lines @@
       'type': 'static_library',
       'sources': [ 'browser/history/in_memory_url_index_cache.proto' ],
       'variables': {
         'proto_in_dir': 'browser/history',
         'proto_out_dir': 'chrome/browser/history',
       },
       'includes': [ '../build/protoc.gypi' ]
     },
   ],
 }