Support alpha channel recording for VPX in MediaRecorder

content/renderer/media_recorder/media_recorder_handler.cc

Index: content/renderer/media_recorder/media_recorder_handler.cc
diff --git a/content/renderer/media_recorder/media_recorder_handler.cc b/content/renderer/media_recorder/media_recorder_handler.cc
index 1055b1537295bba5d04a705cbb40b271b958c77f..9cc45602ffe7e4ce4d5168815c1848651ac9a9eb 100644
--- a/content/renderer/media_recorder/media_recorder_handler.cc
+++ b/content/renderer/media_recorder/media_recorder_handler.cc
@@ -270,6 +270,7 @@ void MediaRecorderHandler::resume() {
 void MediaRecorderHandler::OnEncodedVideo(
     const media::WebmMuxer::VideoParameters& params,
     std::unique_ptr<std::string> encoded_data,
+    std::unique_ptr<std::string> encoded_alpha,
     TimeTicks timestamp,
     bool is_key_frame) {
   DCHECK(main_render_thread_checker_.CalledOnValidThread());
@@ -280,7 +281,8 @@ void MediaRecorderHandler::OnEncodedVideo(
   }
   if (!webm_muxer_)
     return;
-  if (!webm_muxer_->OnEncodedVideo(params, std::move(encoded_data), timestamp,
+  if (!webm_muxer_->OnEncodedVideo(params, std::move(encoded_data),
+                                   std::move(encoded_alpha), timestamp,
                                    is_key_frame)) {
     DLOG(ERROR) << "Error muxing video data";
     client_->onError("Error muxing video data");