Make BrowserMainParts have an empty implementation to make embedding easier.

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/debugger/devtools_resources.gyp:devtools_resources',
     'browser/speech/proto/speech_proto.gyp:speech_proto',
     '../base/base.gyp:base_static',
     '../crypto/crypto.gyp:crypto',
@@ skipping 21 matching lines @@
     'port/browser/render_widget_host_view_port.h',
     'public/browser/access_token_store.h',
     'public/browser/android_library_loader_hooks.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_context.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_shutdown.h',
     'public/browser/browser_url_handler.h',
     'public/browser/browser_thread.h',
     'public/browser/browser_thread_delegate.h',
     'public/browser/cert_store.h',
     'public/browser/child_process_data.h',
@@ skipping 910 matching lines @@
       ],
     }],
     ['input_speech==0', {
       'sources/': [
         ['exclude', '^browser/speech/'],
       ],
     }],
   ],
 }