Implement select listbox using shadow DOM

LayoutTests/platform/mac/fast/forms/listbox-clip-expected.txt

Index: LayoutTests/platform/mac/fast/forms/listbox-clip-expected.txt
diff --git a/LayoutTests/platform/mac/fast/forms/listbox-clip-expected.txt b/LayoutTests/platform/mac/fast/forms/listbox-clip-expected.txt
index a64b3e9652ad6846d5261198d8566af93f2d309c..0aa512371c139f6596e7e4816dbc6528308fb4a7 100644
--- a/LayoutTests/platform/mac/fast/forms/listbox-clip-expected.txt
+++ b/LayoutTests/platform/mac/fast/forms/listbox-clip-expected.txt
@@ -3,5 +3,21 @@ layer at (0,0) size 800x600
 layer at (0,0) size 800x600
   RenderBlock {HTML} at (0,0) size 800x600
     RenderBody {BODY} at (8,8) size 784x584
-      RenderListBox {SELECT} at (0,0) size 100x85 [bgcolor=#FFFFFF] [border: (1px inset #808080)]
       RenderText {#text} at (0,0) size 0x0
+layer at (8,8) size 100x86 clip at (9,9) size 87x84 scrollWidth 122 scrollHeight 105
+  RenderListBox {SELECT} at (0,0) size 100x86 [bgcolor=#FFFFFF] [border: (1px solid #999999)]
+    RenderBlock {OPTION} at (1,1) size 87x21
+      RenderText {#text} at (2,0) size 120x20
+        text run at (2,0) width 120: "aaaaaa"
+    RenderBlock {OPTION} at (1,22) size 87x21
+      RenderText {#text} at (2,0) size 120x20
+        text run at (2,0) width 120: "aaaaaa"
+    RenderBlock {OPTION} at (1,43) size 87x21
+      RenderText {#text} at (2,0) size 120x20
+        text run at (2,0) width 120: "aaaaaa"
+    RenderBlock {OPTION} at (1,64) size 87x21
+      RenderText {#text} at (2,0) size 120x20
+        text run at (2,0) width 120: "aaaaaa"
+    RenderBlock {OPTION} at (1,85) size 87x21
+      RenderText {#text} at (2,0) size 120x20
+        text run at (2,0) width 120: "aaaaaa"