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

content/test/gpu/page_sets/pixel_tests.py

 # Copyright 2014 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.
 # pylint: disable=W0401,W0614
 from telemetry.page.actions.all_page_actions import *
 from telemetry.page import page as page_module
 from telemetry.page import page_set as page_set_module
 
 
 class PixelTestsPage(page_module.Page):
@@ skipping 16 matching lines @@
 class PixelTestsPageSet(page_set_module.PageSet):
 
   """ Some basic test cases for GPU. """
 
   def __init__(self):
     super(PixelTestsPageSet, self).__init__(
       user_agent_type='desktop')
     self.AddPage(PixelTestsPage(
       url='file://../../data/gpu/pixel_canvas2d.html',
       name='Pixel.Canvas2DRedBox',
-      test_rect=[0, 0, 400, 300],
-      revision=2,
+      test_rect=[0, 0, 300, 300],
+      revision=3,
       page_set=self))
 
     self.AddPage(PixelTestsPage(
       url='file://../../data/gpu/pixel_css3d.html',
       name='Pixel.CSS3DBlueBox',
-      test_rect=[0, 0, 400, 300],
-      revision=5,
+      test_rect=[0, 0, 300, 300],
+      revision=6,
       page_set=self))
 
     self.AddPage(PixelTestsPage(
       url='file://../../data/gpu/pixel_webgl.html',
       name='Pixel.WebGLGreenTriangle',
-      test_rect=[0, 0, 400, 300],
-      revision=6,
+      test_rect=[0, 0, 300, 300],
+      revision=7,
       page_set=self))