Modify ImageTransportSurfaceOverlayMac to allow pipelining

gpu/ipc/service/image_transport_surface_overlay_mac.h

 // Copyright 2015 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 GPU_IPC_SERVICE_IMAGE_TRANSPORT_SURFACE_OVERLAY_MAC_H_
 #define GPU_IPC_SERVICE_IMAGE_TRANSPORT_SURFACE_OVERLAY_MAC_H_
 
 #include <list>
 #include <memory>
 #include <vector>
 
 #import "base/mac/scoped_nsobject.h"
 #include "base/timer/timer.h"
 #include "gpu/ipc/service/gpu_command_buffer_stub.h"
 #include "gpu/ipc/service/image_transport_surface.h"
 #include "ui/base/cocoa/remote_layer_api.h"
 #include "ui/events/latency_info.h"
 #include "ui/gl/gl_surface.h"
 #include "ui/gl/gpu_switching_observer.h"
 
 @class CAContext;
 @class CALayer;
 
 namespace ui {
 class CALayerTreeCoordinator;
 }
 
+namespace gl {
+class GLFence;
+}
+
 namespace gpu {
 
 class ImageTransportSurfaceOverlayMac : public gl::GLSurface,
                                         public ui::GpuSwitchingObserver {
  public:
   ImageTransportSurfaceOverlayMac(GpuCommandBufferStub* stub,
                                   SurfaceHandle handle);
 
   // GLSurface implementation
   bool Initialize(gl::GLSurface::Format format) override;
@@ skipping 49 matching lines @@
   std::vector<ui::LatencyInfo> latency_info_;
 
   bool use_remote_layer_api_;
   base::scoped_nsobject<CAContext> ca_context_;
   base::scoped_nsobject<CAContext> fullscreen_low_power_ca_context_;
   std::unique_ptr<ui::CALayerTreeCoordinator> ca_layer_tree_coordinator_;
 
   gfx::Size pixel_size_;
   float scale_factor_;
 
+  std::unique_ptr<gl::GLFence> previous_frame_fence_;
+
   // The renderer ID that all contexts made current to this surface should be
   // targeting.
   GLint gl_renderer_id_;
 };
 
 }  // namespace gpu
 
 #endif  // GPU_IPC_SERVICE_IMAGE_TRANSPORT_SURFACE_OVERLAY_MAC_H_