Iframe/div MD scrollbars get idle when mouse leaves the nested elements.

cc/trees/layer_tree_host_impl.h

 // Copyright 2011 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_LAYER_TREE_HOST_IMPL_H_
 #define CC_TREES_LAYER_TREE_HOST_IMPL_H_
 
 #include <stddef.h>
 
 #include <bitset>
@@ skipping 420 matching lines @@
     return pending_tree_ ? pending_tree_.get() : active_tree_.get();
   }
   virtual void CreatePendingTree();
   virtual void ActivateSyncTree();
 
   // Shortcuts to layers on the active tree.
   LayerImpl* InnerViewportScrollLayer() const;
   LayerImpl* OuterViewportScrollLayer() const;
   LayerImpl* CurrentlyScrollingLayer() const;
 
-  int scroll_layer_id_when_mouse_over_scrollbar() const {
-    return scroll_layer_id_when_mouse_over_scrollbar_;
-  }
   bool scroll_affects_scroll_handler() const {
     return scroll_affects_scroll_handler_;
   }
   void QueueSwapPromiseForMainThreadScrollUpdate(
       std::unique_ptr<SwapPromise> swap_promise);
 
   bool IsActivelyScrolling() const;
 
   virtual void SetVisible(bool visible);
   bool visible() const { return visible_; }
@@ skipping 209 matching lines @@
 
   void UpdateTileManagerMemoryPolicy(const ManagedMemoryPolicy& policy);
 
   // This function should only be called from PrepareToDraw, as DidDrawAllLayers
   // must be called if this helper function is called.  Returns DRAW_SUCCESS if
   // the frame should be drawn.
   DrawResult CalculateRenderPasses(FrameData* frame);
 
   void ClearCurrentlyScrollingLayer();
 
-  void HandleMouseOverScrollbar(LayerImpl* layer_impl);
-
   LayerImpl* FindScrollLayerForDeviceViewportPoint(
       const gfx::PointF& device_viewport_point,
       InputHandler::ScrollInputType type,
       LayerImpl* layer_hit_by_point,
       bool* scroll_on_main_thread,
       uint32_t* main_thread_scrolling_reason) const;
   float DeviceSpaceDistanceToLayer(const gfx::PointF& device_viewport_point,
                                    LayerImpl* layer_impl);
   void StartScrollbarFadeRecursive(LayerImpl* layer);
   void SetManagedMemoryPolicy(const ManagedMemoryPolicy& policy);
@@ skipping 56 matching lines @@
   std::unique_ptr<LayerTreeImpl> pending_tree_;
 
   // In impl-side painting mode, inert tree with layers that can be recycled
   // by the next sync from the main thread.
   std::unique_ptr<LayerTreeImpl> recycle_tree_;
 
   InputHandlerClient* input_handler_client_;
   bool did_lock_scrolling_layer_;
   bool wheel_scrolling_;
   bool scroll_affects_scroll_handler_;
-  int scroll_layer_id_when_mouse_over_scrollbar_;
-  int captured_scrollbar_layer_id_;
+  int scroll_layer_id_mouse_currently_over_;
 
   std::vector<std::unique_ptr<SwapPromise>>
       swap_promises_for_main_thread_scroll_update_;
 
   // An object to implement the ScrollElasticityHelper interface and
   // hold all state related to elasticity. May be NULL if never requested.
   std::unique_ptr<ScrollElasticityHelper> scroll_elasticity_helper_;
 
   bool tile_priorities_dirty_;
 
@@ skipping 77 matching lines @@
 
   std::unique_ptr<PendingTreeDurationHistogramTimer>
       pending_tree_duration_timer_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_IMPL_H_