Bug 980642 - Clean up Compositor::clearFBRect API. r=roc
Bug 980642 - Implement Clear regions for ClientLayerManager/LayerManagerComposite. r=roc
Bug 980642 - Implement ClearRect for CompositorD3D9. r=Bas
Bug 980642 - Implement ClearRect for CompositorD3D11. r=Bas