Handle Alpha channel in Canvas capture

media/base/video_frame.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/base/video_frame.h"
 
 #include <algorithm>
 #include <climits>
 
 #include "base/bind.h"
@@ skipping 839 matching lines @@
   storage_type_ = STORAGE_SHMEM;
   shared_memory_handle_ = handle;
 }
 
 #if defined(OS_MACOSX)
 CVPixelBufferRef VideoFrame::cv_pixel_buffer() const {
   return cv_pixel_buffer_.get();
 }
 #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);
 }
 
 void VideoFrame::UpdateReleaseSyncToken(SyncTokenClient* client) {
   DCHECK(HasTextures());
   base::AutoLock locker(release_sync_token_lock_);
   // Must wait on the previous sync point before inserting a new sync point so
   // that |mailbox_holders_release_cb_| guarantees the previous sync point
@@ skipping 210 matching lines @@
   if (zero_initialize_memory)
     memset(data, 0, data_size);
 
   for (size_t plane = 0; plane < NumPlanes(format_); ++plane)
     data_[plane] = data + offset[plane];
 
   AddDestructionObserver(base::Bind(&base::AlignedFree, data));
 }
 
 }  // namespace media