Update overlay scrollbars

cc/layers/scrollbar_layer_impl_base.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_SCROLLBAR_LAYER_IMPL_BASE_H_
 #define CC_LAYERS_SCROLLBAR_LAYER_IMPL_BASE_H_
 
 #include "cc/base/cc_export.h"
 #include "cc/input/scrollbar.h"
 #include "cc/layers/layer_impl.h"
@@ skipping 46 matching lines @@
 
   float visible_to_total_length_ratio() const {
     return visible_to_total_length_ratio_;
   }
   float vertical_adjust() const { return vertical_adjust_; }
 
   virtual int ThumbThickness() const = 0;
   virtual int ThumbLength() const = 0;
   virtual float TrackLength() const = 0;
   virtual int TrackStart() const = 0;
+  // Indicates whether the thumb length can be changed without going back to the
+  // main thread.
+  virtual bool IsThumbResizable() const = 0;
 
  private:
   int scroll_layer_id_;
   bool is_overlay_scrollbar_;
 
   float thumb_thickness_scale_factor_;
   float current_pos_;
   int maximum_;
   ScrollbarOrientation orientation_;
   bool is_left_side_vertical_scrollbar_;
 
   // Difference between the clip layer's height and the visible viewport
   // height (which may differ in the presence of top-controls hiding).
   float vertical_adjust_;
 
   float visible_to_total_length_ratio_;
 
   DISALLOW_COPY_AND_ASSIGN(ScrollbarLayerImplBase);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_SCROLLBAR_LAYER_IMPL_BASE_H_