Remove mock_ffmpeg and update media unittests.

media/base/video_decoder_config.h

Index: media/base/video_decoder_config.h
diff --git a/media/base/video_decoder_config.h b/media/base/video_decoder_config.h
index a077312e7ed0a63d1b70553b58b6f604aff0e273..541f4378bbb7439fb6288577e1ceecdb56b3e81e 100644
--- a/media/base/video_decoder_config.h
+++ b/media/base/video_decoder_config.h
@@ -30,7 +30,7 @@ class VideoDecoderConfig {
   VideoDecoderConfig(VideoCodec codec, int width, int height,
                      int surface_width, int surface_height,
                      int frame_rate_numerator, int frame_rate_denominator,
-                     uint8* extra_data, size_t extra_data_size);
+                     const uint8* extra_data, size_t extra_data_size);
   ~VideoDecoderConfig();
 
   VideoCodec codec() const;