Check StaticBitmapImage has changed from Mailbox to Skia in OffscreenCanvas commit

third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.cpp

 // Copyright 2016 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 "platform/graphics/OffscreenCanvasFrameDispatcherImpl.h"
 
 #include "cc/output/compositor_frame.h"
 #include "cc/quads/texture_draw_quad.h"
 #include "gpu/command_buffer/client/gles2_interface.h"
 #include "platform/CrossThreadFunctional.h"
@@ skipping 386 matching lines @@
 void OffscreenCanvasFrameDispatcherImpl::OnBeginFrame(
     const cc::BeginFrameArgs& beginFrameArgs) {
   DCHECK(client());
   client()->beginFrame();
 }
 
 void OffscreenCanvasFrameDispatcherImpl::ReclaimResources(
     const cc::ReturnedResourceArray& resources) {
   for (const auto& resource : resources) {
     RefPtr<StaticBitmapImage> image = m_cachedImages.at(resource.id);
-    if (image)
+    // Although image has MailboxTextureHolder at the time when it is
+    // inserted to m_cachedImages, the
+    // OffscreenCanvasPlaceHolder::placeholderFrame() exposes this image to
+    // everyone accessing the placeholder canvas as an image source, some of
+    // which may want to consume the image as a SkImage, thereby converting
+    // the MailTextureHolder to a SkiaTextureHolder. So we must double check
+    // image->hasMailBox() here.
+    if (image && image->hasMailbox())

[Justin Novosad, 2017/03/10 18:41:36]

I don't think this is the right thing to do.  I think SkiaTextureHolder needs to
store the syncToken, And do a WaitSyncToken in its destructor in order to
prevent the texture from being recycled by skia while it is still used by the
compositor.

       image->updateSyncToken(resource.sync_token);
     reclaimResource(resource.id);
   }
 }
 
 void OffscreenCanvasFrameDispatcherImpl::WillDrawSurface(
     const cc::LocalSurfaceId& localSurfaceId,
     ::gfx::mojom::blink::RectPtr damageRect) {
   // TODO(fsamuel, staraz): Implement this.
 }
@@ skipping 23 matching lines @@
 
 void OffscreenCanvasFrameDispatcherImpl::reshape(int width, int height) {
   if (m_width != width || m_height != height) {
     m_width = width;
     m_height = height;
     m_changeSizeForNextCommit = true;
   }
 }
 
 }  // namespace blink