cc: Made image comparison for pixel tests error tolerant.

cc/test/pixel_comparator.h

Index: cc/test/pixel_comparator.h
diff --git a/cc/test/pixel_comparator.h b/cc/test/pixel_comparator.h
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+// Copyright (c) 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.
+
+#ifndef CC_TEST_PIXEL_COMPARATOR_H_
+#define CC_TEST_PIXEL_COMPARATOR_H_
+
+#include "third_party/skia/include/core/SkBitmap.h"
+
+namespace cc {
+
+// Interface for pixel comparators.
+class PixelComparator {
+ public:
+  virtual bool Compare(const SkBitmap& actual_bmp,
+                       const SkBitmap& expected_bmp) const = 0;
+
+ protected:
+  virtual ~PixelComparator() {}
+};
+
+// Exact pixel comparator. Counts the number of pixel with an error.
+class ExactPixelComparator : public PixelComparator {
+ public:
+  // Returns true if the two bitmaps are identical. Otherwise, returns false
+  // and report the number of pixels with an error on LOG(ERROR). Differences
+  // in the alpha channel are ignored.
+  bool Compare(const SkBitmap& actual_bmp, const SkBitmap& expected_bmp) const;
+};
+
+// Fuzzy pixel comparator. Counts small and arbitrary errors separately and
+// computes average and maximum absolute errors per color channel.
+class FuzzyPixelComparator : public PixelComparator {
+ public:
+  FuzzyPixelComparator(const float error_pixels_percentage_limit,
+                       const float small_error_pixels_percentage_limit,
+                       const float avg_abs_error_limit,
+                       const int max_abs_error_limit,
+                       const int small_error_threshold);
+  // Computes error metrics and returns true if the errors don't exceed the
+  // specified limits. Otherwise, returns false and reports the error metrics on
+  // LOG(ERROR). Differences in the alpha channel are ignored.
+  bool Compare(const SkBitmap& actual_bmp, const SkBitmap& expected_bmp) const;
+
+ private:
+  // Limit for percentage of pixels with an error
+  float error_pixels_percentage_limit_;
+  // Limit for percentage of pixels with a small error
+  float small_error_pixels_percentage_limit_;
+  // Limit for average absolute error (excluding identical pixels)
+  float avg_abs_error_limit_;
+  // Limit for largest absolute error
+  int max_abs_error_limit_;
+  // Threshold for small errors
+  int small_error_threshold_;
+};
+
+}  // namespace cc
+
+#endif  // CC_TEST_PIXEL_COMPARATOR_H_