content: convert child process 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 17 matching lines @@
     'public/browser/android/content_view_core.h',
     'public/browser/android/content_view_layer_renderer.h',
     'public/browser/android/devtools_auth.h',
     'public/browser/android/download_controller_android.h',
     'public/browser/browser_accessibility_state.h',
     'public/browser/browser_child_process_host.h',
     'public/browser/browser_child_process_host_delegate.cc',
     'public/browser/browser_child_process_host_delegate.h',
     'public/browser/browser_child_process_host_iterator.cc',
     'public/browser/browser_child_process_host_iterator.h',
+    'public/browser/browser_child_process_observer.cc',
+    'public/browser/browser_child_process_observer.h',
     'public/browser/browser_context.h',
     'public/browser/browser_ipc_logging.h',
     'public/browser/browser_main_parts.cc',
     'public/browser/browser_main_parts.h',
     'public/browser/browser_main_runner.h',
     'public/browser/browser_message_filter.cc',
     'public/browser/browser_message_filter.h',
     'public/browser/browser_ppapi_host.h',
     'public/browser/browser_shutdown.h',
     'public/browser/browser_url_handler.h',
@@ skipping 1173 matching lines @@
         ['exclude', '^browser/speech/'],
       ],
     }],
     ['linux_use_libgps==1', {
       'dependencies': [
         '../build/linux/system.gyp:libgps',
       ],
     }],
   ],
 }