Add ShadowRootInit dictionary.

Source/core/dom/Element.idl

Index: Source/core/dom/Element.idl
diff --git a/Source/core/dom/Element.idl b/Source/core/dom/Element.idl
index ecb8c4a32d91392a8a90892fb78be915839b9fe1..9f580ddafc35c5f967ec83dc40db974f58530752 100644
--- a/Source/core/dom/Element.idl
+++ b/Source/core/dom/Element.idl
@@ -64,7 +64,7 @@
 
     // Shadow DOM
     // http://w3c.github.io/webcomponents/spec/shadow/#extensions-to-element-interface
-    [RaisesException, CallWith=ScriptState, MeasureAs=ElementCreateShadowRoot] ShadowRoot createShadowRoot();
+    [RaisesException, CallWith=ScriptState, MeasureAs=ElementCreateShadowRoot] ShadowRoot createShadowRoot(optional ShadowRootInit shadowRootInitDict);

[hayato, 2015/06/03 08:46:12]

We have to implement this feature as Runtime-Enabled feature. We can't expose
this feature yet.

Also we have to measure the usage of createShadowRoot() and
createShadowRoot(dict) separately so that we can deprecate parameterless
createShadowRoot() in the future.

     NodeList getDestinationInsertionPoints();
     [PerWorldBindings] readonly attribute ShadowRoot? shadowRoot;