Fix scrollbar buttons on ChromeOS.

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

Index: third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp
index b88ec7fdcd07ca9af7ea02d6f244b0144e643356..4391acde0c8626c53125fa6cfd9ce904625ba7d4 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp
@@ -323,8 +323,20 @@ ScrollbarPart ScrollbarThemeAura::invalidateOnThumbPositionChange(const Scrollba
     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);