[PPAPI] Implement media stream video track API

ppapi/thunk/ppb_video_frame_api.h

Index: ppapi/thunk/ppb_video_frame_api.h
diff --git a/ppapi/thunk/ppb_video_frame_api.h b/ppapi/thunk/ppb_video_frame_api.h
index 50f2247ea610890f52156f84b3a5c14fc2b7fa8b..9a088828d1f3f8abe64419a7664f5f49405f4425 100644
--- a/ppapi/thunk/ppb_video_frame_api.h
+++ b/ppapi/thunk/ppb_video_frame_api.h
@@ -9,6 +9,9 @@
 #include "ppapi/thunk/ppapi_thunk_export.h"
 
 namespace ppapi {
+
+union MediaStreamFrame;
+
 namespace thunk {
 
 class PPAPI_THUNK_EXPORT PPB_VideoFrame_API {
@@ -20,6 +23,11 @@ class PPAPI_THUNK_EXPORT PPB_VideoFrame_API {
   virtual PP_Bool GetSize(PP_Size* size) = 0;
   virtual void* GetDataBuffer() = 0;
   virtual uint32_t GetDataBufferSize() = 0;
+
+  // Private APIs:
+  virtual MediaStreamFrame* GetFrameBuffer() = 0;
+  virtual int32_t GetFrameBufferIndex() = 0;
+  virtual void Invalidate() = 0;
 };
 
 }  // namespace thunk