Handle Alpha channel in Canvas capture

media/base/video_frame.cc

Index: media/base/video_frame.cc
diff --git a/media/base/video_frame.cc b/media/base/video_frame.cc
index 4dedd82d10b20633d091bd24aebd31b203c32719..1dba90e427bc5eddfe47f28d17ff963630f92efe 100644
--- a/media/base/video_frame.cc
+++ b/media/base/video_frame.cc
@@ -857,6 +857,22 @@ CVPixelBufferRef VideoFrame::cv_pixel_buffer() const {
 }
 #endif
 
+bool VideoFrame::DropYV12AAlphaChannel() {
+  if (format_ != PIXEL_FORMAT_YV12A) {
+    LOG(DFATAL) << "Only PIXEL_FORMAT_YV12A format supported: "
+                << VideoPixelFormatToString(format_);
+    return false;
+  }
+  if (storage_type_ != STORAGE_OWNED_MEMORY) {
+    LOG(DFATAL) << "Only STORAGE_OWNED_MEMORY format supported.";

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

What about ShMeM? I'd say either 
consider all cases (since alpha can easily 
be nullified for e.g. GMBs etc) or 
just a DCHECK for the supported 
storage types.

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

Adding DCHECKs for supported types.

+    return false;
+  }
+  format_ = PIXEL_FORMAT_I420;
+  data_[kAPlane] = nullptr;
+  strides_[kAPlane] = 0;
+  return true;
+}
+
 void VideoFrame::AddDestructionObserver(const base::Closure& callback) {
   DCHECK(!callback.is_null());
   done_callbacks_.push_back(callback);