Fix cc scrollbar layer issues with initialization, and use element ids throughout.

cc/layers/solid_color_scrollbar_layer.h

 // Copyright 2013 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_LAYERS_SOLID_COLOR_SCROLLBAR_LAYER_H_
 #define CC_LAYERS_SOLID_COLOR_SCROLLBAR_LAYER_H_
 
 #include "base/macros.h"
 #include "cc/cc_export.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/scrollbar_layer_interface.h"
 
 namespace cc {
 
 class CC_EXPORT SolidColorScrollbarLayer : public ScrollbarLayerInterface,
                                            public Layer {
  public:
   std::unique_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl) override;
 
   static scoped_refptr<SolidColorScrollbarLayer> Create(
       ScrollbarOrientation orientation,
       int thumb_thickness,
       int track_start,
       bool is_left_side_vertical_scrollbar,
       ElementId scroll_element_id);
 
   // Layer overrides.
   bool OpacityCanAnimateOnImplThread() const override;
-  bool AlwaysUseActiveTreeOpacity() const override;
   ScrollbarLayerInterface* ToScrollbarLayer() override;
 
   void SetOpacity(float opacity) override;
   void PushPropertiesTo(LayerImpl* layer) override;
 
   void SetNeedsDisplayRect(const gfx::Rect& rect) override;
 
   // ScrollbarLayerInterface
   ElementId scroll_element_id() const override;
   void SetScrollElementId(ElementId element_id) override;
@@ skipping 40 matching lines @@
   };
 
   SolidColorScrollbarLayerInputs solid_color_scrollbar_layer_inputs_;
 
   DISALLOW_COPY_AND_ASSIGN(SolidColorScrollbarLayer);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_SOLID_COLOR_SCROLLBAR_LAYER_H_