Make ui::Snapshot asynchronous on Android, remove CompositeAndReadback.

ui/snapshot/snapshot.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': [
     {
       'target_name': 'snapshot',
       'type': '<(component)',
       'dependencies': [
+        '../../base/base.gyp:base',
+        '../../cc/cc.gyp:cc',
+        '../../gpu/gpu.gyp:command_buffer_common',
         '../../skia/skia.gyp:skia',
-        '../../base/base.gyp:base',
         '../base/ui_base.gyp:ui_base',
         '../gfx/gfx.gyp:gfx',
         '../gfx/gfx.gyp:gfx_geometry',
       ],
       'defines': [
         'SNAPSHOT_IMPLEMENTATION',
       ],
       'sources': [
         'snapshot.h',
         'snapshot_android.cc',
+        'snapshot_async.cc',
+        'snapshot_async.h',
         'snapshot_aura.cc',
         'snapshot_export.h',
         'snapshot_ios.mm',
         'snapshot_mac.mm',
         'snapshot_win.cc',
         'snapshot_win.h',
       ],
       'include_dirs': [
         '..',
       ],
@@ skipping 58 matching lines @@
             'snapshot',
           ],
           'include_dirs': [
             '../..',
           ],
         },
       ],
     }],
   ],
 }