Miscellaneous header file cleanup for src/media.

media/ffmpeg/ffmpeg_common.h

Index: media/ffmpeg/ffmpeg_common.h
diff --git a/media/ffmpeg/ffmpeg_common.h b/media/ffmpeg/ffmpeg_common.h
index bb01f4f12e3b246a59deab1b81bf3b04e49b6513..13a53cfad2fb832af2d235593689d33d20d22f97 100644
--- a/media/ffmpeg/ffmpeg_common.h
+++ b/media/ffmpeg/ffmpeg_common.h
@@ -9,13 +9,10 @@
 #include <cerrno>
 
 #include "base/compiler_specific.h"
-#include "base/memory/singleton.h"
 #include "base/time.h"
-#include "media/base/audio_decoder_config.h"
 #include "media/base/channel_layout.h"
 #include "media/base/media_export.h"
-#include "media/video/video_decode_engine.h"
-#include "ui/gfx/size.h"
+#include "media/base/video_frame.h"
 
 // Include FFmpeg header files.
 extern "C" {
@@ -32,6 +29,9 @@ MSVC_POP_WARNING();
 
 namespace media {
 
+class AudioDecoderConfig;
+class VideoDecoderConfig;
+
 // Wraps FFmpeg's av_free() in a class that can be passed as a template argument
 // to scoped_ptr_malloc.
 class ScopedPtrAVFree {