[Cast] Software encoder support for varying video frame sizes.

media/cast/test/utility/video_utility.h

 // Copyright 2014 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.
 
 // Utility functions for video testing.
 
 #include "media/base/video_frame.h"
 
 namespace media {
 namespace cast {
 
 // Compute and return PSNR between two frames.
 double I420PSNR(const scoped_refptr<media::VideoFrame>& frame1,
                 const scoped_refptr<media::VideoFrame>& frame2);
 
 // Compute and return SSIM between two frames.
 double I420SSIM(const scoped_refptr<media::VideoFrame>& frame1,
                 const scoped_refptr<media::VideoFrame>& frame2);
 
-// Populate a video frame with values starting with the given start value.
+// Populate a video |frame| with a plaid pattern, cycling from the given
+// |start_value|.
 // Width, height and stride should be set in advance.
 // Memory is allocated within the function.
 void PopulateVideoFrame(VideoFrame* frame, int start_value);
 
 // Populate a video frame with noise.
 void PopulateVideoFrameWithNoise(VideoFrame* frame);
 
 // Populate a video frame from a file.
 // Returns true if frame was populated, false if not (EOF).
 bool PopulateVideoFrameFromFile(VideoFrame* frame, FILE* video_file);
 
 }  // namespace cast
 }  // namespace media