aura: Remove CreateOffscreenContext from ui::ContextFactory.

ui/compositor/compositor.gyp

 # 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
@@ skipping 12 matching lines @@
       'defines': [
         'COMPOSITOR_IMPLEMENTATION',
       ],
       'sources': [
         'compositor.cc',
         'compositor.h',
         'compositor_export.h',
         'compositor_observer.h',
         'compositor_switches.cc',
         'compositor_switches.h',
-        'context_provider_from_context_factory.cc',
-        'context_provider_from_context_factory.h',
         'debug_utils.cc',
         'debug_utils.h',
         'dip_util.cc',
         'dip_util.h',
         'float_animation_curve_adapter.cc',
         'float_animation_curve_adapter.h',
         'layer.cc',
         'layer.h',
         'layer_animation_delegate.h',
         'layer_animation_element.cc',
@@ skipping 97 matching lines @@
               'dependencies': [
                 '<(DEPTH)/base/allocator/allocator.gyp:allocator',
               ],
             }],
           ],
         }],
       ],
     },
   ],
 }