Handle Alpha channel in Canvas capture

content/renderer/pepper/pepper_video_source_host.cc

Index: content/renderer/pepper/pepper_video_source_host.cc
diff --git a/content/renderer/pepper/pepper_video_source_host.cc b/content/renderer/pepper/pepper_video_source_host.cc
index db20126b141a6f30c413748970c36a7bb5f36e5d..37ec156dc9acbb3ef135517d7719f237bfc2275a 100644
--- a/content/renderer/pepper/pepper_video_source_host.cc
+++ b/content/renderer/pepper/pepper_video_source_host.cc
@@ -59,6 +59,18 @@ void PepperVideoSourceHost::FrameReceiver::GotFrame(
   DCHECK(thread_checker_.CalledOnValidThread());
   if (!host_)
     return;
+
+  if (!(frame->IsMappable() &&
+        (frame->format() == media::PIXEL_FORMAT_I420 ||
+         frame->format() == media::PIXEL_FORMAT_YV12A))) {
+    NOTREACHED();
+    return;
+  }
+
+  // Drop alpha channel since we do not support it yet.
+  if (frame->format() == media::PIXEL_FORMAT_YV12A)
+    frame->DropYV12AAlphaChannel();
+
   // Hold a reference to the new frame and release the previous.
   host_->last_frame_ = frame;
   if (host_->get_frame_pending_)