[DevTools] Extract DeviceModeButton from AdvancedApp.

Source/devtools/devtools.gypi

 #
 # Copyright (C) 2013 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #         * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #         * Redistributions in binary form must reproduce the above
@@ skipping 187 matching lines @@
             'front_end/platform/utilities.js',
         ],
         'devtools_toolbox_bootstrap_js_files': [
             'front_end/toolbox_bootstrap/Toolbox.js',
         ],
         'devtools_emulation_js_files': [
             'front_end/emulation/accelerometer.css',
             'front_end/emulation/devicesSettingsTab.css',
             'front_end/emulation/overrides.css',
             'front_end/emulation/responsiveDesignView.css',
+            'front_end/emulation/DeviceModeButton.js',
             'front_end/emulation/DevicesSettingsTab.js',
             'front_end/emulation/EmulatedDevices.js',
             'front_end/emulation/InspectedPagePlaceholder.js',
             'front_end/emulation/MediaQueryInspector.js',
             'front_end/emulation/OverridesSupport.js',
             'front_end/emulation/OverridesView.js',
             'front_end/emulation/OverridesUI.js',
             'front_end/emulation/ResponsiveDesignView.js',
         ],
         'devtools_ui_js_files': [
@@ skipping 534 matching lines @@
             'front_end/Images/toolbarItemSelected.png',
             'front_end/Images/touchCursor.png',
             'front_end/Images/touchCursor_2x.png',
             'front_end/Images/updateServiceWorker.svg',
         ],
         'devtools_extension_api_files': [
             'front_end/extensions/ExtensionAPI.js',
         ],
     },
 }