[cc] Fix CompositorFrameSinkSupport BeginFrameAck interface.

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

 // 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.
 
 #ifndef OffscreenCanvasFrameDispatcherImpl_h
 #define OffscreenCanvasFrameDispatcherImpl_h
 
 #include <memory>
 #include "cc/ipc/mojo_compositor_frame_sink.mojom-blink.h"
 #include "cc/output/begin_frame_args.h"
@@ skipping 62 matching lines @@
   HashSet<unsigned> m_spareResourceLocks;
 
   bool verifyImageSize(const IntSize);
   void postImageToPlaceholder(RefPtr<StaticBitmapImage>);
 
   cc::mojom::blink::MojoCompositorFrameSinkPtr m_sink;
   mojo::Binding<cc::mojom::blink::MojoCompositorFrameSinkClient> m_binding;
 
   int m_placeholderCanvasId;
 
+  cc::BeginFrameAck m_currentBeginFrameAck;
+
   void setTransferableResourceToSharedBitmap(cc::TransferableResource&,
                                              RefPtr<StaticBitmapImage>);
   void setTransferableResourceToSharedGPUContext(cc::TransferableResource&,
                                                  RefPtr<StaticBitmapImage>);
   void setTransferableResourceToStaticBitmapImage(cc::TransferableResource&,
                                                   RefPtr<StaticBitmapImage>);
 };
 
 }  // namespace blink
 
 #endif  // OffscreenCanvasFrameDispatcherImpl_h