Improve Aura overdraw by changing hole calculation

ui/gfx/compositor/layer.h

Index: ui/gfx/compositor/layer.h
diff --git a/ui/gfx/compositor/layer.h b/ui/gfx/compositor/layer.h
index f98021de9ef6f64612a9a03d25e695afd62bcb01..a410e6e2394ad5d41614d5bc329f84372ed3082a 100644
--- a/ui/gfx/compositor/layer.h
+++ b/ui/gfx/compositor/layer.h
@@ -185,6 +185,15 @@ class COMPOSITOR_EXPORT Layer : public LayerAnimatorDelegate {
   // delegate.
   void UpdateLayerCanvas();
 
+  // Resets |hole_rect_| to the empty rect for all layers below and
+  // including this one.
+  void ClearHoleRects();
+
+  // Does a preorder traversal of layers starting with this layer. Omits layers
+  // which cannot punch a hole in  another layer such as non visible layers

[sky, 2011/10/24 15:44:52]

'in  another' -> 'in another'

+  // and layers which don't fill their bounds opaquely.
+  void GeneratePreorderTraversal(std::vector<ui::Layer*>* layer_traversal);
+
   // A hole in a layer is an area in the layer that does not get drawn
   // because this area is covered up with another layer which is known to be
   // opaque.
@@ -194,9 +203,9 @@ class COMPOSITOR_EXPORT Layer : public LayerAnimatorDelegate {
   // view has no transform with respect to its parent.
   void RecomputeHole();
 
-  // Returns true if the layer paints every pixel (fills_bounds_opaquely)
-  // and the alpha of the layer is 1.0f.
-  bool IsCompletelyOpaque() const;
+  void set_hole_rect(const gfx::Rect& hole_rect) {
+    hole_rect_ = hole_rect;
+  }
 
   // Determines the regions that don't intersect |rect| and places the
   // result in |sides|.
@@ -216,6 +225,9 @@ class COMPOSITOR_EXPORT Layer : public LayerAnimatorDelegate {
                         const gfx::Rect& region_to_punch_out,
                         std::vector<gfx::Rect>* sides);
 
+  // Drops texture just for this layer.
+  void DropTexture();
+
   // Drop all textures for layers below and including this one. Called when
   // the layer is removed from a hierarchy. Textures will be re-generated if
   // the layer is subsequently re-attached and needs to be drawn.