Disable overlay scrollbars in Blink when hidden by the compositor.

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 387 matching lines @@
   bool operator==(const ScrollTree& other) const;
 
   void ToProtobuf(proto::PropertyTree* proto) const;
   void FromProtobuf(const proto::PropertyTree& proto,
                     std::unordered_map<int, int>* node_id_to_index_map);
 
   void clear();
 
   typedef std::unordered_map<int, scoped_refptr<SyncedScrollOffset>>
       ScrollOffsetMap;
+  typedef std::unordered_map<int, bool> ScrollbarsEnabledMap;
 
   gfx::ScrollOffset MaxScrollOffset(int scroll_node_id) const;
   void OnScrollOffsetAnimated(int layer_id,
                               int transform_tree_index,
                               int scroll_tree_index,
                               const gfx::ScrollOffset& scroll_offset,
                               LayerTreeImpl* layer_tree_impl);
   gfx::Size scroll_clip_layer_bounds(int scroll_node_id) const;
   ScrollNode* CurrentlyScrollingNode();
   const ScrollNode* CurrentlyScrollingNode() const;
@@ skipping 28 matching lines @@
   void DistributeScroll(ScrollNode* scroll_node, ScrollState* scroll_state);
   gfx::Vector2dF ScrollBy(ScrollNode* scroll_node,
                           const gfx::Vector2dF& scroll,
                           LayerTreeImpl* layer_tree_impl);
   gfx::ScrollOffset ClampScrollOffsetToLimits(gfx::ScrollOffset offset,
                                               ScrollNode* scroll_node) const;
 
  private:
   int currently_scrolling_node_id_;
   ScrollOffsetMap layer_id_to_scroll_offset_map_;
+  ScrollbarsEnabledMap layer_id_to_scrollbars_enabled_map_;
 
   SyncedScrollOffset* synced_scroll_offset(int layer_id);
   const SyncedScrollOffset* synced_scroll_offset(int layer_id) const;
   gfx::ScrollOffset PullDeltaForMainThread(SyncedScrollOffset* scroll_offset);
   void UpdateScrollOffsetMapEntry(int key,
                                   ScrollOffsetMap* new_scroll_offset_map,
                                   LayerTreeImpl* layer_tree_impl);
 };
 
 struct AnimationScaleData {
@@ skipping 188 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_