Fix scrollbar buttons on ChromeOS.

ui/native_theme/native_theme.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/native_theme/native_theme.h"
 
 #include <cstring>
 
 #include "ui/native_theme/native_theme_observer.h"
 
 namespace ui {
 
 NativeTheme::ExtraParams::ExtraParams() {
   memset(this, 0, sizeof(*this));
 }
 
 NativeTheme::ExtraParams::ExtraParams(const ExtraParams& other) {
   memcpy(this, &other, sizeof(*this));
 }
 
+bool NativeTheme::HasScrollbarButtons() const {
+  return true;
+}
+
 void NativeTheme::SetScrollbarColors(unsigned inactive_color,
                                      unsigned active_color,
                                      unsigned track_color) {
   thumb_inactive_color_ = inactive_color;
   thumb_active_color_ = active_color;
   track_color_ = track_color;
 }
 
 void NativeTheme::AddObserver(NativeThemeObserver* observer) {
   native_theme_observers_.AddObserver(observer);
@@ skipping 10 matching lines @@
 
 NativeTheme::NativeTheme()
     : thumb_inactive_color_(0xeaeaea),
       thumb_active_color_(0xf4f4f4),
       track_color_(0xd3d3d3) {
 }
 
 NativeTheme::~NativeTheme() {}
 
 }  // namespace ui