Handle Alpha channel in Canvas capture

content/renderer/media/video_track_recorder.cc

Index: content/renderer/media/video_track_recorder.cc
diff --git a/content/renderer/media/video_track_recorder.cc b/content/renderer/media/video_track_recorder.cc
index 82ae3ea9ba7dc9ed25e19f9277f1e0fd758de253..8cddb2653b44b0134007801f42f67f0c093b7f61 100644
--- a/content/renderer/media/video_track_recorder.cc
+++ b/content/renderer/media/video_track_recorder.cc
@@ -192,6 +192,17 @@ void VideoTrackRecorder::VpxEncoder::EncodeOnEncodingThread(
                "VideoTrackRecorder::VpxEncoder::EncodeOnEncodingThread");
   DCHECK(encoding_thread_->task_runner()->BelongsToCurrentThread());
 
+  if (!(frame->IsMappable() &&

[mcasas, 2016/02/25 22:06:25]

Why add this here now? (Same elsewhere).

[emircan, 2016/02/26 01:33:08]

Removing IsMappable() checks.

+        (frame->format() == media::PIXEL_FORMAT_I420 ||
+         frame->format() == media::PIXEL_FORMAT_YV12A))) {
+    NOTREACHED();
+    return;
+  }

[mcasas, 2016/02/25 22:06:25]

Judgment call: turn this into a DCHECK() and
let it continue? AFAIK there's nothing but I420
frames on the renderer MSs before this CL.

[emircan, 2016/02/26 01:33:08]

I actually started with DCHECKs but then found [0], so I decided to follow the
pattern. I know that DCHECKs would be better for performance, but there might be
cases out in the wild that isn't covered by the current tests. It is a hard
judgment call. WDYT?

[0]
https://code.google.com/p/chromium/codesearch#chromium/src/content/renderer/m...

+
+  // Drop alpha channel since we do not support it yet.
+  if (frame->format() == media::PIXEL_FORMAT_YV12A)
+    frame->DropYV12AAlphaChannel();
+
   const gfx::Size frame_size = frame->visible_rect().size();
   if (!IsInitialized() ||
       gfx::Size(codec_config_.g_w, codec_config_.g_h) != frame_size) {