Fix build issue of missing BackingStrategy vtable.

content/common/gpu/media/android_video_decode_accelerator.h

Index: content/common/gpu/media/android_video_decode_accelerator.h
diff --git a/content/common/gpu/media/android_video_decode_accelerator.h b/content/common/gpu/media/android_video_decode_accelerator.h
index 7c3a28a3e5a8ccfb4dbd5ec1653742203d69ee40..ea4f6e8641b6246e27c8270d93093f1cbc2195be 100644
--- a/content/common/gpu/media/android_video_decode_accelerator.h
+++ b/content/common/gpu/media/android_video_decode_accelerator.h
@@ -105,7 +105,7 @@ class CONTENT_EXPORT AndroidVideoDecodeAccelerator
     // associated texture). Callers should set the correct GL context prior to
     // calling.
     virtual void UpdatePictureBufferSize(media::PictureBuffer* picture_buffer,
-                                         const gfx::Size& new_size);
+                                         const gfx::Size& new_size) = 0;
   };
 
   AndroidVideoDecodeAccelerator(