cc : Replace unordered_maps with flat_map in property trees

cc/trees/property_tree.h

 // 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.
 
 #ifndef CC_TREES_PROPERTY_TREE_H_
 #define CC_TREES_PROPERTY_TREE_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 489 matching lines @@
 
   const SyncedScrollOffset* GetSyncedScrollOffset(int layer_id) const;
 
 #if DCHECK_IS_ON()
   void CopyCompleteTreeState(const ScrollTree& other);
 #endif
 
   ScrollNode* FindNodeFromElementId(ElementId id);
 
  private:
-  using ScrollOffsetMap = std::unordered_map<int, gfx::ScrollOffset>;
+  using ScrollOffsetMap = base::flat_map<int, gfx::ScrollOffset>;
   using SyncedScrollOffsetMap =
-      std::unordered_map<int, scoped_refptr<SyncedScrollOffset>>;
+      base::flat_map<int, scoped_refptr<SyncedScrollOffset>>;
 
   int currently_scrolling_node_id_;
 
   // On the main thread we store the scroll offsets directly since the main
   // thread only needs to keep track of the current main thread state. The impl
   // thread stores a map of SyncedProperty instances in order to track
   // additional state necessary to synchronize scroll changes between the main
   // and impl threads.
   ScrollOffsetMap layer_id_to_scroll_offset_map_;
   SyncedScrollOffsetMap layer_id_to_synced_scroll_offset_map_;
@@ skipping 116 matching lines @@
 
   bool operator==(const PropertyTrees& other) const;
   PropertyTrees& operator=(const PropertyTrees& from);
 
   // These maps allow mapping directly from a compositor element id to the
   // respective property node. This will eventually allow simplifying logic in
   // various places that today has to map from element id to layer id, and then
   // from layer id to the respective property node. Completing that work is
   // pending the launch of Slimming Paint v2 and reworking UI compositor logic
   // to produce cc property trees and these maps.
-  std::unordered_map<ElementId, int, ElementIdHash>
-      element_id_to_effect_node_index;
-  std::unordered_map<ElementId, int, ElementIdHash>
-      element_id_to_scroll_node_index;
-  std::unordered_map<ElementId, int, ElementIdHash>
-      element_id_to_transform_node_index;
+  base::flat_map<ElementId, int> element_id_to_effect_node_index;
+  base::flat_map<ElementId, int> element_id_to_scroll_node_index;
+  base::flat_map<ElementId, int> element_id_to_transform_node_index;
 
   std::vector<int> always_use_active_tree_opacity_effect_ids;
   TransformTree transform_tree;
   EffectTree effect_tree;
   ClipTree clip_tree;
   ScrollTree scroll_tree;
   bool needs_rebuild;
   bool non_root_surfaces_enabled;
   bool can_adjust_raster_scales;
   // Change tracking done on property trees needs to be preserved across commits
@@ skipping 66 matching lines @@
   DrawTransforms& GetDrawTransforms(int transform_id, int effect_id) const;
   DrawTransformData& FetchDrawTransformsDataFromCache(int transform_id,
                                                       int effect_id) const;
 
   PropertyTreesCachedData cached_data_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_PROPERTY_TREE_H_