Use Microsoft's HMFT for VP9 decoding.

media/gpu/dxva_video_decode_accelerator_win.h

Index: media/gpu/dxva_video_decode_accelerator_win.h
diff --git a/media/gpu/dxva_video_decode_accelerator_win.h b/media/gpu/dxva_video_decode_accelerator_win.h
index 852d02a91e2711c65932e4f3a17a8bca08e5b6a0..92eddf3d053abcaa6f9cd43a85811b183f33aa28 100644
--- a/media/gpu/dxva_video_decode_accelerator_win.h
+++ b/media/gpu/dxva_video_decode_accelerator_win.h
@@ -476,6 +476,9 @@ class MEDIA_GPU_EXPORT DXVAVideoDecodeAccelerator
   // H/W decoding.
   bool use_dx11_;
 
+  // True when using Microsoft's VP9 HMFT for decoding.
+  bool using_ms_vp9_mft_ = false;
+
   // True if we should use DXGI keyed mutexes to synchronize between the two
   // contexts.
   bool use_keyed_mutex_;