cc: Made image comparison for pixel tests error tolerant.

cc/test/layer_tree_pixel_test.cc

 // Copyright 2013 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.
 
 #include "cc/test/layer_tree_pixel_test.h"
 
 #include "base/path_service.h"
 #include "cc/test/paths.h"
 #include "cc/test/pixel_test_utils.h"
 #include "cc/trees/layer_tree_impl.h"
@@ skipping 48 matching lines @@
   bitmap.allocPixels();
   unsigned char* pixels = static_cast<unsigned char*>(bitmap.getPixels());
   host_impl->Readback(pixels, device_viewport_rect);
 
   base::FilePath test_data_dir;
   EXPECT_TRUE(PathService::Get(cc::DIR_TEST_DATA, &test_data_dir));
 
   // To rebaseline:
   // EXPECT_TRUE(WritePNGFile(bitmap, test_data_dir.Append(ref_file_)));
 
-  EXPECT_TRUE(IsSameAsPNGFile(bitmap, test_data_dir.Append(ref_file_), true));
+  EXPECT_TRUE(MatchesPNGFile(bitmap, test_data_dir.Append(ref_file_),
+                             ExactPixelComparator(true)));
 
   EndTest();
 }
 
 void LayerTreePixelTest::BeginTest() {
   PostSetNeedsCommitToMainThread();
 }
 
 void LayerTreePixelTest::AfterTest() {}
 
@@ skipping 18 matching lines @@
 
 void LayerTreePixelTest::SetupTree() {
   scoped_refptr<Layer> root = Layer::Create();
   root->SetBounds(content_root_->bounds());
   root->AddChild(content_root_);
   layer_tree_host()->SetRootLayer(root);
   LayerTreeTest::SetupTree();
 }
 
 }  // namespace cc