2D Canvas doesn't blend video with the destination buffer.

cc/resources/video_resource_updater.cc

 // Copyright 2013 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 "cc/resources/video_resource_updater.h"
 
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
 #include "cc/output/gl_renderer.h"
 #include "cc/resources/resource_provider.h"
@@ skipping 231 matching lines @@
     DCHECK_EQ(plane_resources.size(), 1u);
     DCHECK_EQ(plane_resources[0].resource_format, kRGBResourceFormat);
     DCHECK(plane_resources[0].mailbox.IsZero());
 
     if (!video_renderer_)
       video_renderer_.reset(new media::SkCanvasVideoRenderer);
 
     {
       ResourceProvider::ScopedWriteLockSoftware lock(
           resource_provider_, plane_resources[0].resource_id);
+      // Clear because reusing the resource among frames.
+      lock.sk_canvas()->clear(SK_ColorTRANSPARENT);
       video_renderer_->Paint(video_frame.get(),
                              lock.sk_canvas(),
                              video_frame->visible_rect(),
                              0xff);
     }
 
     RecycleResourceData recycle_data = {
       plane_resources[0].resource_id,
       plane_resources[0].resource_size,
       plane_resources[0].resource_format,
@@ skipping 129 matching lines @@
   }
 
   PlaneResource recycled_resource(data.resource_id,
                                   data.resource_size,
                                   data.resource_format,
                                   data.mailbox);
   updater->recycled_resources_.push_back(recycled_resource);
 }
 
 }  // namespace cc