Share backing canvases between browser compositors.

content/browser/compositor/gpu_process_transport_factory.h

Index: content/browser/compositor/gpu_process_transport_factory.h
diff --git a/content/browser/compositor/gpu_process_transport_factory.h b/content/browser/compositor/gpu_process_transport_factory.h
index 54f02ef29511c998c36e58cf51a0a73fec614c9f..171c030f4e5bae8b9d39701b3b0b0c2e776e24fd 100644
--- a/content/browser/compositor/gpu_process_transport_factory.h
+++ b/content/browser/compositor/gpu_process_transport_factory.h
@@ -22,6 +22,7 @@ class Thread;
 }
 
 namespace cc {
+class SoftwareOutputDevice;
 class SurfaceManager;
 }
 
@@ -29,6 +30,7 @@ namespace content {
 class BrowserCompositorOutputSurface;
 class CompositorSwapClient;
 class ContextProviderCommandBuffer;
+class OutputDeviceBacking;
 class ReflectorImpl;
 class WebGraphicsContext3DCommandBufferImpl;
 
@@ -78,6 +80,8 @@ class GpuProcessTransportFactory
   struct PerCompositorData;
 
   PerCompositorData* CreatePerCompositorData(ui::Compositor* compositor);
+  scoped_ptr<cc::SoftwareOutputDevice> CreateSoftwareOutputDevice(
+      ui::Compositor* compositor);
   void EstablishedGpuChannel(base::WeakPtr<ui::Compositor> compositor,
                              bool create_gpu_output_surface,
                              int num_attempts);
@@ -98,6 +102,10 @@ class GpuProcessTransportFactory
   scoped_ptr<cc::TaskGraphRunner> task_graph_runner_;
   scoped_ptr<base::SimpleThread> raster_thread_;
 
+#if defined(OS_WIN)
+  scoped_ptr<OutputDeviceBacking> software_backing_;
+#endif
+
   // The contents of this map and its methods may only be used on the compositor
   // thread.
   IDMap<BrowserCompositorOutputSurface> output_surface_map_;