Introduce content::ChildMessageFilter.

content/content_child.gypi

 # Copyright 2013 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': [
     '../base/base.gyp:base',
     '../components/tracing.gyp:tracing',
     '../skia/skia.gyp:skia',
     '../ui/gfx/gfx.gyp:gfx',
@@ skipping 14 matching lines @@
     'child/appcache/appcache_dispatcher.cc',
     'child/appcache/appcache_dispatcher.h',
     'child/appcache/appcache_frontend_impl.cc',
     'child/appcache/appcache_frontend_impl.h',
     'child/appcache/web_application_cache_host_impl.cc',
     'child/appcache/web_application_cache_host_impl.h',
     'child/browser_font_resource_trusted.cc',
     'child/browser_font_resource_trusted.h',
     'child/child_histogram_message_filter.cc',
     'child/child_histogram_message_filter.h',
+    'child/child_message_filter.cc',
+    'child/child_message_filter.h',
     'child/child_process.cc',
     'child/child_process.h',
     'child/child_resource_message_filter.cc',
     'child/child_resource_message_filter.h',
     'child/child_thread.cc',
     'child/child_thread.h',
     'child/database_util.cc',
     'child/database_util.h',
     'child/db_message_filter.cc',
     'child/db_message_filter.h',
@@ skipping 142 matching lines @@
         'child/npapi/webplugin_delegate_impl_mac.mm',
       ],
     }],
     ['use_aura==1 and OS=="win"', {
       'sources!': [
         'child/npapi/webplugin_delegate_impl_aura.cc',
       ],
     }],
   ],
 }