Update from https://crrev.com/316786

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.h"
@@ skipping 33 matching lines @@
     return is_left_side_vertical_scrollbar_;
   }
 
   bool CanScrollOrientation() const;
 
   void PushPropertiesTo(LayerImpl* layer) override;
   ScrollbarLayerImplBase* ToScrollbarLayer() override;
   void PushScrollClipPropertiesTo(LayerImpl* layer);
 
   bool SetVisibleToTotalLengthRatio(float ratio);
+  // Thumb quad rect in layer space.
   virtual gfx::Rect ComputeThumbQuadRect() const;
 
   float thumb_thickness_scale_factor() {
     return thumb_thickness_scale_factor_;
   }
   bool SetThumbThicknessScaleFactor(float thumb_thickness_scale_factor);
 
   void ScrollbarParametersDidChange(bool on_resize);
 
  protected:
@@ skipping 35 matching lines @@
   float vertical_adjust_;
 
   float visible_to_total_length_ratio_;
 
   DISALLOW_COPY_AND_ASSIGN(ScrollbarLayerImplBase);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_SCROLLBAR_LAYER_IMPL_BASE_H_