Split picture layer quads to allow removing more occluded area.

cc/trees/occlusion.h

Index: cc/trees/occlusion.h
diff --git a/cc/trees/occlusion.h b/cc/trees/occlusion.h
index ea38304907fb6f39edd21dd082f61eea91e18baf..a059c1a92e979f2f58d69193f52e1f19ae4606fc 100644
--- a/cc/trees/occlusion.h
+++ b/cc/trees/occlusion.h
@@ -26,6 +26,7 @@ class CC_EXPORT Occlusion {
   bool HasOcclusion() const;
   bool IsOccluded(const gfx::Rect& content_rect) const;
   gfx::Rect GetUnoccludedContentRect(const gfx::Rect& content_rect) const;
+  void OccludeContentRegion(Region* region) const;
 
   bool IsEqual(const Occlusion& other) const;
   std::string ToString() const;
@@ -35,6 +36,8 @@ class CC_EXPORT Occlusion {
       const gfx::Rect& content_rect) const;
 
   gfx::Transform draw_transform_;
+  mutable gfx::Transform inverse_draw_transform_;
+  mutable bool inverse_transform_initialized_ = false;
   SimpleEnclosedRegion occlusion_from_outside_target_;
   SimpleEnclosedRegion occlusion_from_inside_target_;
 };