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

content/renderer/media/rtc_video_decoder.cc

Index: content/renderer/media/rtc_video_decoder.cc
diff --git a/content/renderer/media/rtc_video_decoder.cc b/content/renderer/media/rtc_video_decoder.cc
index 302d5d5ef85add26ab23afea2c15ebc7a04bf37a..123a90ebfb208de73ae3650c43e53658dc9215b6 100644
--- a/content/renderer/media/rtc_video_decoder.cc
+++ b/content/renderer/media/rtc_video_decoder.cc
@@ -384,8 +384,12 @@ void RTCVideoDecoder::PictureReady(const media::Picture& picture) {
     return;
   }
 
+  media::VideoPixelFormat pixel_format = vda_->GetOutputFormat();
+  if (pixel_format == media::PIXEL_FORMAT_UNKNOWN)
+    pixel_format = media::PIXEL_FORMAT_ARGB;
+
   scoped_refptr<media::VideoFrame> frame =
-      CreateVideoFrame(picture, pb, timestamp, visible_rect);
+      CreateVideoFrame(picture, pb, timestamp, visible_rect, pixel_format);
   if (!frame) {
     NotifyError(media::VideoDecodeAccelerator::PLATFORM_FAILURE);
     return;
@@ -416,19 +420,21 @@ scoped_refptr<media::VideoFrame> RTCVideoDecoder::CreateVideoFrame(
     const media::Picture& picture,
     const media::PictureBuffer& pb,
     uint32_t timestamp,
-    const gfx::Rect& visible_rect) {
+    const gfx::Rect& visible_rect,
+    media::VideoPixelFormat pixel_format) {
   DCHECK(decoder_texture_target_);
   // Convert timestamp from 90KHz to ms.
   base::TimeDelta timestamp_ms = base::TimeDelta::FromInternalValue(
       base::checked_cast<uint64_t>(timestamp) * 1000 / 90);
-  // TODO(mcasas): The incoming data is actually a YUV format, but is labelled
-  // as ARGB. This prevents the compositor from messing with it, since the
-  // underlying platform can handle the former format natively. Make sure the
+  // TODO(mcasas): The incoming data may actually be in a YUV format, but may be
+  // labelled as ARGB. This may or may not be reported by VDA, depending on
+  // whether it provides an implementation of VDA::GetOutputFormat().
+  // This prevents the compositor from messing with it, since the underlying
+  // platform can handle the former format natively. Make sure the
   // correct format is used and everyone down the line understands it.
   scoped_refptr<media::VideoFrame> frame = media::VideoFrame::WrapNativeTexture(
-      media::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_),
       media::BindToCurrentLoop(base::Bind(
           &RTCVideoDecoder::ReleaseMailbox, weak_factory_.GetWeakPtr(),
           factories_, picture.picture_buffer_id(), pb.texture_ids()[0])),