Add NULL check for NativeTheme in scrollbar methods. A NULL theme can

ui/views/controls/scrollbar/native_scroll_bar_views.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/native_scroll_bar_views.h"
 
 #include "base/logging.h"
 #include "ui/base/keycodes/keyboard_codes.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/path.h"
@@ skipping 364 matching lines @@
 
 // static
 NativeScrollBarWrapper* NativeScrollBarWrapper::CreateWrapper(
     NativeScrollBar* scroll_bar) {
   return new NativeScrollBarViews(scroll_bar);
 }
 
 // static
 int NativeScrollBarWrapper::GetHorizontalScrollBarHeight(
     const ui::NativeTheme* theme) {
+  if (!theme)
+    theme = ui::NativeTheme::instance();
   ui::NativeTheme::ExtraParams button_params;
   button_params.scrollbar_arrow.is_hovering = false;
   gfx::Size button_size = theme->GetPartSize(
       ui::NativeTheme::kScrollbarLeftArrow,
       ui::NativeTheme::kNormal,
       button_params);
 
   ui::NativeTheme::ExtraParams thumb_params;
   thumb_params.scrollbar_thumb.is_hovering = false;
   gfx::Size track_size = theme->GetPartSize(
       ui::NativeTheme::kScrollbarHorizontalThumb,
       ui::NativeTheme::kNormal,
       thumb_params);
 
   return std::max(track_size.height(), button_size.height());
 }
 
 // static
 int NativeScrollBarWrapper::GetVerticalScrollBarWidth(
     const ui::NativeTheme* theme) {
+  if (!theme)
+    theme = ui::NativeTheme::instance();
   ui::NativeTheme::ExtraParams button_params;
   button_params.scrollbar_arrow.is_hovering = false;
   gfx::Size button_size = theme->GetPartSize(
       ui::NativeTheme::kScrollbarUpArrow,
       ui::NativeTheme::kNormal,
       button_params);
 
   ui::NativeTheme::ExtraParams thumb_params;
   thumb_params.scrollbar_thumb.is_hovering = false;
   gfx::Size track_size = theme->GetPartSize(
       ui::NativeTheme::kScrollbarVerticalThumb,
       ui::NativeTheme::kNormal,
       thumb_params);
 
   return std::max(track_size.width(), button_size.width());
 }
 
 }  // namespace views