Switch to LayoutThemeMobile when emulating mobile device in DevTools.

third_party/WebKit/Source/build/features.gypi

 #
 # Copyright (C) 2009 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 52 matching lines @@
         'feature_defines': [
           'WTF_USE_LOW_QUALITY_IMAGE_INTERPOLATION=1'
         ],
       }, { # OS!=android
         'feature_defines': [
           'ENABLE_INPUT_MULTIPLE_FIELDS_UI=1',
           'WTF_USE_ICCJPEG=1',
           'WTF_USE_QCMSLIB=1'
         ],
       }],
-      ['OS=="mac"', {
-        'feature_defines': [
-          'WTF_USE_NEW_THEME=1'
-        ],
-      }],
       # Mac OS X uses Accelerate.framework FFT by default instead of FFmpeg.
       ['OS!="mac" and OS!="android"', {
         'feature_defines': [
           'WTF_USE_WEBAUDIO_FFMPEG=1',
         ],
       }],
       ['OS=="android" and use_openmax_dl_fft!=0', {
         'feature_defines': [
           'WTF_USE_WEBAUDIO_OPENMAX_DL_FFT=1',
         ],
@@ skipping 17 matching lines @@
         'feature_defines': [
           'LINK_CORE_MODULES_SEPARATELY',
         ],
       }],
     ],
 
     # shared build only. If set to 1, link web, core and modules separately.
     'link_core_modules_separately%': '<(link_core_modules_separately)',
   },
 }