Improve DamageTracker performance.

cc/trees/damage_tracker.h

Index: cc/trees/damage_tracker.h
diff --git a/cc/trees/damage_tracker.h b/cc/trees/damage_tracker.h
index fbcaa69824df97de458e29d2c0c81fd1a315834b..eb7bf1b8dcff1113a4c0f52ff368fe8571e22b9b 100644
--- a/cc/trees/damage_tracker.h
+++ b/cc/trees/damage_tracker.h
@@ -53,21 +53,29 @@ class CC_EXPORT DamageTracker {
   gfx::RectF TrackDamageFromSurfaceMask(LayerImpl* target_surface_mask_layer);
   gfx::RectF TrackDamageFromLeftoverRects();
 
-  gfx::RectF RemoveRectFromCurrentFrame(int layer_id, bool* layer_is_new);
-  void SaveRectForNextFrame(int layer_id, const gfx::RectF& target_space_rect);
+  void PrepareRectHistoryForUpdate();
 
   // These helper functions are used only in TrackDamageFromActiveLayers().
   void ExtendDamageForLayer(LayerImpl* layer, gfx::RectF* target_damage_rect);
   void ExtendDamageForRenderSurface(LayerImpl* layer,
                                     gfx::RectF* target_damage_rect);
 
-  // To correctly track exposed regions, two hashtables of rects are maintained.
-  // The "current" map is used to compute exposed regions of the current frame,
-  // while the "next" map is used to collect layer rects that are used in the
-  // next frame.
-  typedef base::hash_map<int, gfx::RectF> RectMap;
-  scoped_ptr<RectMap> current_rect_history_;
-  scoped_ptr<RectMap> next_rect_history_;
+  struct  RectMapData {

[danakj, 2013/11/21 00:13:40]

formatting is off, please run git cl format on the CL.

[ostap, 2013/11/21 17:06:23]

Great! Didn't know about "cl format"!

Done

+      RectMapData() : updated_(false) {}
+      void Update(const gfx::RectF& rect) {
+        rect_ = rect;
+        updated_ = true;
+      }
+
+      gfx::RectF rect_;
+      bool updated_;
+
+    };
+  typedef base::hash_map<int, RectMapData> RectMap;
+
+  RectMapData& RectDataForLayer(int layer_id, bool* layer_is_new);
+
+  RectMap rect_history_;
 
   gfx::RectF current_damage_rect_;