Implement select listbox using shadow DOM

LayoutTests/fast/forms/option-mouseevents-expected.txt

Index: LayoutTests/fast/forms/option-mouseevents-expected.txt
diff --git a/LayoutTests/fast/forms/option-mouseevents-expected.txt b/LayoutTests/fast/forms/option-mouseevents-expected.txt
index 87460efba115ebbc23c263cb2e80eac9087d3216..4c5bbd51e7e230d009456093c807eea553187fa0 100644
--- a/LayoutTests/fast/forms/option-mouseevents-expected.txt
+++ b/LayoutTests/fast/forms/option-mouseevents-expected.txt
@@ -10,64 +10,64 @@ PASS: event type should be mousedown and is
 PASS: event target should be [object HTMLOptionElement] and is
 PASS: event.pageX should be 22 and is
 PASS: event.pageY should be 104 and is
-PASS: event.offsetX should be 22 and is
-PASS: event.offsetY should be 104 and is
+PASS: event.offsetX should be 13 and is
+PASS: event.offsetY should be 5 and is
 PASS: event.x should be 22 and is
 PASS: event.y should be 104 and is
 PASS: event type should be mousedown and is
 PASS: event target should be [object HTMLOptionElement] and is
 PASS: event.pageX should be 22 and is
 PASS: event.pageY should be 104 and is
-PASS: event.offsetX should be 22 and is
-PASS: event.offsetY should be 104 and is
+PASS: event.offsetX should be 13 and is
+PASS: event.offsetY should be 5 and is
 PASS: event.x should be 22 and is
 PASS: event.y should be 104 and is
 PASS: event type should be mouseup and is
 PASS: event target should be [object HTMLOptionElement] and is
 PASS: event.pageX should be 22 and is
 PASS: event.pageY should be 184 and is
-PASS: event.offsetX should be 22 and is
-PASS: event.offsetY should be 184 and is
+PASS: event.offsetX should be 13 and is
+PASS: event.offsetY should be 5 and is
 PASS: event.x should be 22 and is
 PASS: event.y should be 184 and is
 PASS: event type should be mouseup and is
 PASS: event target should be [object HTMLOptionElement] and is
 PASS: event.pageX should be 22 and is
 PASS: event.pageY should be 184 and is
-PASS: event.offsetX should be 22 and is
-PASS: event.offsetY should be 184 and is
+PASS: event.offsetX should be 13 and is
+PASS: event.offsetY should be 5 and is
 PASS: event.x should be 22 and is
 PASS: event.y should be 184 and is
 PASS: event type should be click and is
 PASS: event target should be [object HTMLOptionElement] and is
 PASS: event.pageX should be 22 and is
 PASS: event.pageY should be 262 and is
-PASS: event.offsetX should be 22 and is
-PASS: event.offsetY should be 262 and is
+PASS: event.offsetX should be 13 and is
+PASS: event.offsetY should be 5 and is
 PASS: event.x should be 22 and is
 PASS: event.y should be 262 and is
 PASS: event type should be click and is
 PASS: event target should be [object HTMLOptionElement] and is
 PASS: event.pageX should be 22 and is
 PASS: event.pageY should be 262 and is
-PASS: event.offsetX should be 22 and is
-PASS: event.offsetY should be 262 and is
+PASS: event.offsetX should be 13 and is
+PASS: event.offsetY should be 5 and is
 PASS: event.x should be 22 and is
 PASS: event.y should be 262 and is
 PASS: event type should be dblclick and is
 PASS: event target should be [object HTMLOptionElement] and is
 PASS: event.pageX should be 22 and is
 PASS: event.pageY should be 344 and is
-PASS: event.offsetX should be 22 and is
-PASS: event.offsetY should be 344 and is
+PASS: event.offsetX should be 13 and is
+PASS: event.offsetY should be 5 and is
 PASS: event.x should be 22 and is
 PASS: event.y should be 344 and is
 PASS: event type should be dblclick and is
 PASS: event target should be [object HTMLOptionElement] and is
 PASS: event.pageX should be 22 and is
 PASS: event.pageY should be 344 and is
-PASS: event.offsetX should be 22 and is
-PASS: event.offsetY should be 344 and is
+PASS: event.offsetX should be 13 and is
+PASS: event.offsetY should be 5 and is
 PASS: event.x should be 22 and is
 PASS: event.y should be 344 and is
 PASS: event type should be mousedown and is