Reland of: cc: Add occlusion checker as a fixed view of occlusion tracker.

cc/trees/occlusion_tracker.h

 // Copyright 2012 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_TRACKER_H_
 #define CC_TREES_OCCLUSION_TRACKER_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
 #include "cc/base/cc_export.h"
 #include "cc/base/simple_enclosed_region.h"
 #include "cc/layers/layer_iterator.h"
+#include "cc/trees/occlusion.h"
 #include "ui/gfx/rect.h"
 
 namespace cc {
 class LayerImpl;
 class Region;
 class RenderSurfaceImpl;
 class Layer;
 class RenderSurface;
 
 // This class is used to track occlusion of layers while traversing them in a
 // front-to-back order. As each layer is visited, one of the methods in this
 // class is called to notify it about the current target surface. Then,
 // occlusion in the content space of the current layer may be queried, via
 // methods such as Occluded() and UnoccludedContentRect(). If the current layer
 // owns a RenderSurfaceImpl, then occlusion on that RenderSurfaceImpl may also
 // be queried via surfaceOccluded() and surfaceUnoccludedContentRect(). Finally,
 // once finished with the layer, occlusion behind the layer should be marked by
 // calling MarkOccludedBehindLayer().
 template <typename LayerType>
 class CC_EXPORT OcclusionTracker {
  public:
   explicit OcclusionTracker(const gfx::Rect& screen_space_clip_rect);
   ~OcclusionTracker();
 
+  // Return an occlusion that retains the current state of the tracker
+  // and can be used outside of a layer walk to check occlusion.
+  Occlusion GetCurrentOcclusionForLayer(
+      const gfx::Transform& draw_transform) const;
+
   // Called at the beginning of each step in the LayerIterator's front-to-back
   // traversal.
   void EnterLayer(const LayerIteratorPosition<LayerType>& layer_iterator);
   // Called at the end of each step in the LayerIterator's front-to-back
   // traversal.
   void LeaveLayer(const LayerIteratorPosition<LayerType>& layer_iterator);
 
   // Returns true if the given rect in content space for a layer is fully
   // occluded in either screen space or the layer's target surface.
   // |render_target| is the contributing layer's render target, and
@@ skipping 89 matching lines @@
 };
 
 #if !defined(COMPILER_MSVC)
 extern template class OcclusionTracker<Layer>;
 extern template class OcclusionTracker<LayerImpl>;
 #endif
 
 }  // namespace cc
 
 #endif  // CC_TREES_OCCLUSION_TRACKER_H_