Fix scrollbar buttons on ChromeOS.

third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp

 /*
  * Copyright (c) 2008, 2009, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 305 matching lines @@
     ScrollbarPart invalidParts = NoPart;
     ASSERT(buttonsPlacement() == WebScrollbarButtonsPlacementSingle);
     static const ScrollbarPart kButtonParts[] = {BackButtonStartPart, ForwardButtonEndPart};
     for (ScrollbarPart part : kButtonParts) {
         if (buttonPartPaintingParams(scrollbar, oldPosition, part) != buttonPartPaintingParams(scrollbar, newPosition, part))
             invalidParts = static_cast<ScrollbarPart>(invalidParts | part);
     }
     return invalidParts;
 }
 
+bool ScrollbarThemeAura::hasScrollbarButtons(ScrollbarOrientation orientation) const
+{
+    WebThemeEngine* themeEngine = Platform::current()->themeEngine();
+    if (orientation == VerticalScrollbar) {
+        return !themeEngine->getSize(WebThemeEngine::PartScrollbarDownArrow).isEmpty();
+    }
+    return !themeEngine->getSize(WebThemeEngine::PartScrollbarLeftArrow).isEmpty();
+};
+
 IntSize ScrollbarThemeAura::buttonSize(const ScrollbarThemeClient& scrollbar)
 {
+    if (!hasScrollbarButtons(scrollbar.orientation()))
+        return IntSize(0, 0);
+
     if (scrollbar.orientation() == VerticalScrollbar) {
         int squareSize = scrollbar.width();
         return IntSize(squareSize, scrollbar.height() < 2 * squareSize ? scrollbar.height() / 2 : squareSize);
     }
 
     // HorizontalScrollbar
     int squareSize = scrollbar.height();
     return IntSize(scrollbar.width() < 2 * squareSize ? scrollbar.width() / 2 : squareSize, squareSize);
 }
 
 } // namespace blink