Track where WebContents are created in order to better understand issue.

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': [
     '../base/base.gyp:base_static',
     '../components/url_formatter/url_formatter.gyp:url_formatter',
     '../crypto/crypto.gyp:crypto',
     '../device/battery/battery.gyp:device_battery',
@@ skipping 266 matching lines @@
       'public/browser/url_data_source.cc',
       'public/browser/url_data_source.h',
       'public/browser/user_metrics.h',
       'public/browser/utility_process_host.h',
       'public/browser/web_contents.cc',
       'public/browser/web_contents.h',
       'public/browser/web_contents_delegate.cc',
       'public/browser/web_contents_delegate.h',
       'public/browser/web_contents_observer.cc',
       'public/browser/web_contents_observer.h',
+      'public/browser/web_contents_source.cc',
+      'public/browser/web_contents_source.h',
       'public/browser/web_contents_user_data.h',
       'public/browser/web_contents_view_delegate.cc',
       'public/browser/web_contents_view_delegate.h',
       'public/browser/web_drag_dest_delegate.h',
       'public/browser/web_ui.h',
       'public/browser/web_ui_controller.cc',
       'public/browser/web_ui_controller.h',
       'public/browser/web_ui_controller_factory.h',
       'public/browser/web_ui_data_source.h',
       'public/browser/web_ui_message_handler.h',
@@ skipping 1878 matching lines @@
     ['enable_webvr==1 and OS=="android"', {
       'sources': [
         'browser/vr/android/cardboard/cardboard_vr_device.cc',
         'browser/vr/android/cardboard/cardboard_vr_device.h',
         'browser/vr/android/cardboard/cardboard_vr_device_provider.cc',
         'browser/vr/android/cardboard/cardboard_vr_device_provider.h',
       ],
     }],
   ],
 }