Fix darkened pixels when rendering using GPU

content/test/gpu/gpu_tests/pixel_test_pages.py

 # Copyright 2016 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.
 
 class PixelTestPage(object):
   """A wrapper class mimicking the functionality of the PixelTestsStorySet
   from the old-style GPU tests.
   """
   def __init__(self, url, name, test_rect, revision,
                tolerance=2, browser_args=None, expected_colors=None):
@@ skipping 37 matching lines @@
 
 def DefaultPages(base_name):
   return [
     PixelTestPage(
       'pixel_canvas2d.html',
       base_name + '_Canvas2DRedBox',
       test_rect=[0, 0, 300, 300],
       revision=7),
 
     PixelTestPage(
+      'pixel_canvas2d_untagged.html',
+      base_name + '_Canvas2DUntagged',
+      test_rect=[0, 0, 257, 257],
+      revision=0),
+
+    PixelTestPage(
       'pixel_css3d.html',
       base_name + '_CSS3DBlueBox',
       test_rect=[0, 0, 300, 300],
       revision=16),
 
     PixelTestPage(
       'pixel_webgl_aa_alpha.html',
       base_name + '_WebGLGreenTriangle_AA_Alpha',
       test_rect=[0, 0, 300, 300],
       revision=1),
@@ skipping 430 matching lines @@
       revision=2,
       browser_args=browser_args),
 
     PixelTestPage(
       'pixel_video_vp9.html',
       base_name + '_DirectComposition_Video_VP9',
       test_rect=[0, 0, 300, 300],
       revision=2,
       browser_args=browser_args),
   ]