Make GPU back-pressure work with remote CALayers

content/common/gpu/image_transport_surface_fbo_mac.h

Index: content/common/gpu/image_transport_surface_fbo_mac.h
diff --git a/content/common/gpu/image_transport_surface_fbo_mac.h b/content/common/gpu/image_transport_surface_fbo_mac.h
index 3587e21b0b3a86f84d7d6f26843a479609bf6915..42f6683498c48317c6cd8fbf16ad23cb8aafb33b 100644
--- a/content/common/gpu/image_transport_surface_fbo_mac.h
+++ b/content/common/gpu/image_transport_surface_fbo_mac.h
@@ -45,12 +45,19 @@ class ImageTransportSurfaceFBO
     // display.
     virtual uint64 GetSurfaceHandle() const = 0;
 
-    // Called when a frame is about to be sent to the browser process.
+    // Called when a new frame has been rendered into the texture, and the
+    // browser is about to be sent the surface to display.
     virtual void WillSwapBuffers() = 0;
+
+    // Called once for every WillSwapBuffers call when the buffer that was sent
+    // to the browser may be released by the GPU process (this may be because
+    // the browser is holding a reference, in which case this will come
+    // quickly, or it may be because the browser is done with the surface, in
+    // which case it will come much later).
+    virtual void CanFreeSwappedBuffer() = 0;
   };
 
-  ImageTransportSurfaceFBO(StorageProvider* storage_provider,
-                           GpuChannelManager* manager,
+  ImageTransportSurfaceFBO(GpuChannelManager* manager,
                            GpuCommandBufferStub* stub,
                            gfx::PluginWindowHandle handle);
 
@@ -70,6 +77,9 @@ class ImageTransportSurfaceFBO
   virtual bool SetBackbufferAllocation(bool allocated) OVERRIDE;
   virtual void SetFrontbufferAllocation(bool allocated) OVERRIDE;
 
+  // Called when the context may continue to make forward progress after a swap.
+  void UnblockContextAfterPendingSwap();
+
  protected:
   // ImageTransportSurface implementation
   virtual void OnBufferPresented(