cc : Clean up cc clip tree

cc/trees/property_tree.cc

Index: cc/trees/property_tree.cc
diff --git a/cc/trees/property_tree.cc b/cc/trees/property_tree.cc
index af6e451a922933eaa1d66b458e59543d8fe6b343..f99a3a7ac32fcef753135c51bb80d294b4080262 100644
--- a/cc/trees/property_tree.cc
+++ b/cc/trees/property_tree.cc
@@ -2036,6 +2036,17 @@ DrawTransformData& PropertyTrees::FetchDrawTransformsDataFromCache(
   return data;
 }
 
+ClipRectData& PropertyTrees::FetchClipRectFromCache(int clip_id,

[weiliangc, 2017/03/14 22:04:30]

Could we return pointer here to make cache miss more obvious? Does that affect
performance?

[jaydasika, 2017/03/16 20:33:31]

I haven't tried it, so I don't know if it effects performance. I will change it
to a pointer. The reason I did not choose a pointer in the first place is I was
trying to make this function similar to FetchDrawTransformsFromCache 

+                                                    int target_id) {
+  ClipNode* clip_node = clip_tree.Node(clip_id);
+  for (auto& data : clip_node->cached_clip_rects) {
+    if (data.target_id == target_id || data.target_id == -1)
+      return data;
+  }
+  clip_node->cached_clip_rects.push_back(ClipRectData());
+  return clip_node->cached_clip_rects.back();
+}
+
 DrawTransforms& PropertyTrees::GetDrawTransforms(int transform_id,
                                                  int effect_id) const {
   const EffectNode* effect_node = effect_tree.Node(effect_id);