Remove DOMImplementation.createCSSStyleSheet()

LayoutTests/fast/dom/StyleSheet/gc-parent-stylesheet.html

Index: LayoutTests/fast/dom/StyleSheet/gc-parent-stylesheet.html
diff --git a/LayoutTests/fast/dom/StyleSheet/gc-parent-stylesheet.html b/LayoutTests/fast/dom/StyleSheet/gc-parent-stylesheet.html
index 518e15a6812cebd0eb724b0ee6018b94a6bdd53e..3bd3e182232202502d2a36a1c0a3f4eb947bff99 100644
--- a/LayoutTests/fast/dom/StyleSheet/gc-parent-stylesheet.html
+++ b/LayoutTests/fast/dom/StyleSheet/gc-parent-stylesheet.html
@@ -7,9 +7,20 @@
 window.jsTestIsAsync = true;
 description("Test that CSS stylesheets don't lose custom properties on GC when only reachable through child rules.");
 
+function createCSSStyleSheet()
+{
+    style = document.createElement("style");
+    document.head.appendChild(style);
+    shouldBeType("style.sheet", "CSSStyleSheet");
+    var sheet = style.sheet;
+    document.head.removeChild(style);
+    shouldBeNull("style.sheet");
+    return sheet;
+}
+
 function test()
 {
-    var sheet = document.implementation.createCSSStyleSheet("title", "screen");
+    var sheet = createCSSStyleSheet();
     sheet.foo = "0";
     sheet.insertRule("div { color:black }", 0);
     rule = sheet.rules[0];