[Chromoting] Add a unit test to verify that the VP8 codec doesn't change color values too much.

remoting/base/codec_test.h

 // Copyright (c) 2011 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 REMOTING_BASE_CODEC_TEST_H_
 #define REMOTING_BASE_CODEC_TEST_H_
 
 #include "base/memory/ref_counted.h"
 #include "media/base/video_frame.h"
 #include "remoting/base/capture_data.h"
@@ skipping 14 matching lines @@
 // If |strict| is set to true then this routine will make sure the updated
 // rects match dirty rects.
 void TestEncoder(Encoder* encoder, bool strict);
 
 // Generate test data and test the encoder and decoder pair.
 //
 // If |strict| is set to true, this routine will make sure the updated rects
 // are correct.
 void TestEncoderDecoder(Encoder* encoder, Decoder* decoder, bool strict);
 
+// Generate a frame containing a gradient, and test the encoder and decoder
+// pair.
+void TestEncoderDecoderGradient(Encoder* encoder, Decoder* decoder,
+                                double max_error_limit,
+                                double mean_error_limit);
+
 }  // namespace remoting
 
 #endif  // REMOTING_BASE_CODEC_TEST_H_