Update comments about scrollbar thickness.

third_party/WebKit/Source/core/paint/ThemePainterDefault.cpp

Index: third_party/WebKit/Source/core/paint/ThemePainterDefault.cpp
diff --git a/third_party/WebKit/Source/core/paint/ThemePainterDefault.cpp b/third_party/WebKit/Source/core/paint/ThemePainterDefault.cpp
index 1ce8c7c30fdfea97f048d5527940c1fe8ca5a702..d90765de589248818df3dd327af7fdec3115a320 100644
--- a/third_party/WebKit/Source/core/paint/ThemePainterDefault.cpp
+++ b/third_party/WebKit/Source/core/paint/ThemePainterDefault.cpp
@@ -290,7 +290,7 @@ void ThemePainterDefault::setupMenuListArrow(
   extraParams.menuList.arrowY = middle;
   float arrowBoxWidth = m_theme.clampedMenuListArrowPaddingSize(
       box.frameView()->getHostWindow(), box.styleRef());
-  float arrowScaleFactor = arrowBoxWidth / m_theme.scrollbarThicknessInDIP();
+  float arrowScaleFactor = arrowBoxWidth / m_theme.menuListArrowWidthInDIP();
   if (useMockTheme()) {
     // The size and position of the drop-down button is different between
     // the mock theme and the regular aura theme.