Implement Sebastien's overlay scrollbars for native UI (Views).

ui/views/controls/scrollbar/base_scroll_bar.cc

 // Copyright (c) 2012 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.
 
 #include "ui/views/controls/scrollbar/base_scroll_bar.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback.h"
 #include "base/compiler_specific.h"
@@ skipping 389 matching lines @@
     contents_scroll_offset = 0;
   if (contents_scroll_offset > content_size)
     contents_scroll_offset = content_size;
   contents_scroll_offset_ = contents_scroll_offset;
 
   // Thumb Height and Thumb Pos.
   // The height of the thumb is the ratio of the Viewport height to the
   // content size multiplied by the height of the thumb track.
   double ratio =
       std::min(1.0, static_cast<double>(viewport_size) / contents_size_);
-  int thumb_size = static_cast<int>(ratio * GetTrackSize());
-  thumb_->SetSize(thumb_size);
+  thumb_->SetLength(static_cast<int>(ratio * GetTrackSize()));
 
   int thumb_position = CalculateThumbPosition(contents_scroll_offset);
   thumb_->SetPosition(thumb_position);
 }
 
 int BaseScrollBar::GetPosition() const {
   return thumb_->GetPosition();
 }
 
 ///////////////////////////////////////////////////////////////////////////////
@@ skipping 84 matching lines @@
   return (thumb_position * (contents_size_ - viewport_size_)) /
          (track_size - thumb_size);
 }
 
 void BaseScrollBar::SetThumbTrackState(CustomButton::ButtonState state) {
   thumb_track_state_ = state;
   SchedulePaint();
 }
 
 }  // namespace views