cc: Don't draw and swap if the frame will not change.

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 a5c1c544ec2e7826145c295d0b0f7f1d806b5fbf..474667391204fda7d2fea3b6b5e29262fdf6b83a 100644
--- a/cc/trees/damage_tracker.h
+++ b/cc/trees/damage_tracker.h
@@ -35,7 +35,7 @@ class CC_EXPORT DamageTracker {
   ~DamageTracker();
 
   void DidDrawDamagedArea() { current_damage_rect_ = gfx::RectF(); }
-  void ForceFullDamageNextUpdate() { force_full_damage_next_update_ = true; }
+  void AddDamageNextUpdate(gfx::RectF dmg) { current_damage_rect_.Union(dmg); }
   void UpdateDamageTrackingState(
       const std::vector<LayerImpl*>& layer_list,
       int target_surface_layer_id,
@@ -73,7 +73,6 @@ class CC_EXPORT DamageTracker {
   scoped_ptr<RectMap> next_rect_history_;
 
   gfx::RectF current_damage_rect_;
-  bool force_full_damage_next_update_;
 
   DISALLOW_COPY_AND_ASSIGN(DamageTracker);
 };