cc : Clean up cc clip tree

cc/trees/property_tree.cc

 // Copyright 2014 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.
 
 #include <stddef.h>
 
 #include <set>
 #include <vector>
 
 #include "base/logging.h"
@@ skipping 2018 matching lines @@
     }
   }
   // Add an entry to the cache.
   cached_data_.draw_transforms[transform_id].push_back(DrawTransformData());
   DrawTransformData& data = cached_data_.draw_transforms[transform_id].back();
   data.update_number = -1;
   data.target_id = dest_id;
   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);
   int dest_id = effect_node->transform_id;
 
   DrawTransformData& data =
       FetchDrawTransformsDataFromCache(transform_id, dest_id);
 
   DCHECK(data.update_number != cached_data_.transform_tree_update_number ||
          data.target_id != EffectTree::kInvalidNodeId);
@@ skipping 65 matching lines @@
   const EffectNode* effect_node = effect_tree.Node(effect_id);
 
   if (effect_node->surface_contents_scale.x() != 0.0 &&
       effect_node->surface_contents_scale.y() != 0.0)
     screen_space_transform.Scale(1.0 / effect_node->surface_contents_scale.x(),
                                  1.0 / effect_node->surface_contents_scale.y());
   return screen_space_transform;
 }
 
 }  // namespace cc