Split picture layer quads to allow removing more occluded area.

cc/trees/occlusion.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_TREES_OCCLUSION_H_
 #define CC_TREES_OCCLUSION_H_
 
 #include <string>
 
 #include "cc/base/simple_enclosed_region.h"
 #include "cc/cc_export.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/transform.h"
 
 namespace cc {
 
 class CC_EXPORT Occlusion {
  public:
   Occlusion();
   Occlusion(const gfx::Transform& draw_transform,
             const SimpleEnclosedRegion& occlusion_from_outside_target,
             const SimpleEnclosedRegion& occlusion_from_inside_target);
   Occlusion GetOcclusionWithGivenDrawTransform(
       const gfx::Transform& transform) const;
 
   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;
 
  private:
   gfx::Rect GetUnoccludedRectInTargetSurface(
       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_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_OCCLUSION_H_