cc: Made image comparison for pixel tests error tolerant.

cc/test/pixel_test.h

Index: cc/test/pixel_test.h
diff --git a/cc/test/pixel_test.h b/cc/test/pixel_test.h
index 3762d60692e4384a33f08d177e4d04e74ec2ce9d..e915961097335a1c9d0b97ff86ef6098d45d4f03 100644
--- a/cc/test/pixel_test.h
+++ b/cc/test/pixel_test.h
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "base/file_util.h"
+#include "cc/test/pixel_comparator.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gfx/size.h"
 
@@ -22,7 +23,7 @@ class PixelTest : public testing::Test {
   virtual void SetUp() OVERRIDE;
 
   bool PixelsMatchReference(const base::FilePath& ref_file,
-      bool discard_transparency);
+                            const PixelComparator& comparator);
 
   gfx::Size device_viewport_size_;
   scoped_ptr<OutputSurface> output_surface_;