Implement select listbox using shadow DOM

Source/core/rendering/RenderLayerScrollableArea.cpp

Index: Source/core/rendering/RenderLayerScrollableArea.cpp
diff --git a/Source/core/rendering/RenderLayerScrollableArea.cpp b/Source/core/rendering/RenderLayerScrollableArea.cpp
index 0836796d528931cd5e75334855e21c9a7116c1b2..0bc0c3b9321dace6da60cd6fbdd1222a04f448b8 100644
--- a/Source/core/rendering/RenderLayerScrollableArea.cpp
+++ b/Source/core/rendering/RenderLayerScrollableArea.cpp
@@ -59,6 +59,7 @@
 #include "core/rendering/RenderGeometryMap.h"
 #include "core/rendering/RenderScrollbar.h"
 #include "core/rendering/RenderScrollbarPart.h"
+#include "core/rendering/RenderTheme.h"
 #include "core/rendering/RenderView.h"
 #include "core/rendering/compositing/CompositedLayerMapping.h"
 #include "core/rendering/compositing/RenderLayerCompositor.h"
@@ -568,10 +569,6 @@ void RenderLayerScrollableArea::scrollToOffset(const IntSize& scrollOffset, Scro
 
 void RenderLayerScrollableArea::updateAfterLayout()
 {
-    // List box parts handle the scrollbars by themselves so we have nothing to do.
-    if (box().style()->appearance() == ListboxPart)
-        return;
-
     m_scrollDimensionsDirty = true;
     IntSize originalScrollOffset = adjustedScrollOffset();
 
@@ -696,10 +693,6 @@ static bool overflowDefinesAutomaticScrollbar(EOverflow overflow)
 
 void RenderLayerScrollableArea::updateAfterStyleChange(const RenderStyle* oldStyle)
 {
-    // List box parts handle the scrollbars by themselves so we have nothing to do.
-    if (box().style()->appearance() == ListboxPart)
-        return;
-
     // RenderView shouldn't provide scrollbars on its own.
     if (box().isRenderView())
         return;
@@ -847,7 +840,10 @@ PassRefPtr<Scrollbar> RenderLayerScrollableArea::createScrollbar(ScrollbarOrient
     if (hasCustomScrollbarStyle) {
         widget = RenderScrollbar::createCustomScrollbar(this, orientation, actualRenderer->node());
     } else {
-        widget = Scrollbar::create(this, orientation, RegularScrollbar);
+        ScrollbarControlSize scrollbarSize = RegularScrollbar;
+        if (actualRenderer->style()->hasAppearance())
+            scrollbarSize = RenderTheme::theme().scrollbarControlSizeForPart(actualRenderer->style()->appearance());
+        widget = Scrollbar::create(this, orientation, scrollbarSize);
         if (orientation == HorizontalScrollbar)
             didAddScrollbar(widget.get(), HorizontalScrollbar);
         else