[WIP] Implement BackGroundFilter as seperate layer in cc

cc/output/software_renderer.h

Index: cc/output/software_renderer.h
diff --git a/cc/output/software_renderer.h b/cc/output/software_renderer.h
index 5c9fef0ba57d9cf94cb08428c004b5d716a44eb7..52358fc2786d033323deabc4ab67e0bd91486160 100644
--- a/cc/output/software_renderer.h
+++ b/cc/output/software_renderer.h
@@ -19,6 +19,7 @@ class SoftwareOutputDevice;
 
 class CheckerboardDrawQuad;
 class DebugBorderDrawQuad;
+class FilterDrawQuad;
 class PictureDrawQuad;
 class RenderPassDrawQuad;
 class SolidColorDrawQuad;
@@ -92,6 +93,7 @@ class CC_EXPORT SoftwareRenderer : public DirectRenderer {
                     const TileDrawQuad* quad);
   void DrawUnsupportedQuad(const DrawingFrame* frame,
                            const DrawQuad* quad);
+  void DrawFilterQuad(const DrawingFrame* frame, const FilterDrawQuad* quad);
 
   RendererCapabilitiesImpl capabilities_;
   bool is_scissor_enabled_;