Support external buffer import in VDA interface and add a V4L2SVDA impl.

media/filters/gpu_video_decoder.cc

Index: media/filters/gpu_video_decoder.cc
diff --git a/media/filters/gpu_video_decoder.cc b/media/filters/gpu_video_decoder.cc
index 2e11d8786863c034b87f05dd097905f068276d53..6149959c173305ce4abadb109c5d4caaeda1dd65 100644
--- a/media/filters/gpu_video_decoder.cc
+++ b/media/filters/gpu_video_decoder.cc
@@ -541,12 +541,15 @@ void GpuVideoDecoder::PictureReady(const media::Picture& picture) {
 
   DCHECK(decoder_texture_target_);
 
-  bool opaque = IsOpaque(config_.format());
+  VideoPixelFormat pixel_format = vda_->GetOutputFormat();
+  if (pixel_format == PIXEL_FORMAT_UNKNOWN) {
+    pixel_format =
+        IsOpaque(config_.format()) ? PIXEL_FORMAT_XRGB : PIXEL_FORMAT_ARGB;
+  }
 
   scoped_refptr<VideoFrame> frame(VideoFrame::WrapNativeTexture(
-      opaque ? PIXEL_FORMAT_XRGB : PIXEL_FORMAT_ARGB,
-      gpu::MailboxHolder(pb.texture_mailbox(0), gpu::SyncToken(),
-                         decoder_texture_target_),
+      pixel_format, gpu::MailboxHolder(pb.texture_mailbox(0), gpu::SyncToken(),
+                                       decoder_texture_target_),
       BindToCurrentLoop(base::Bind(
           &GpuVideoDecoder::ReleaseMailbox, weak_factory_.GetWeakPtr(),
           factories_, picture.picture_buffer_id(), pb.texture_ids())),