Set default document urls to 'about:blank'.

third_party/WebKit/Source/core/dom/Document.idl

Index: third_party/WebKit/Source/core/dom/Document.idl
diff --git a/third_party/WebKit/Source/core/dom/Document.idl b/third_party/WebKit/Source/core/dom/Document.idl
index 68a3907d9215aa857f098c0365f1fb9457f5e0e2..575e6400345c334b22eb6b06349abb35860fa16a 100644
--- a/third_party/WebKit/Source/core/dom/Document.idl
+++ b/third_party/WebKit/Source/core/dom/Document.idl
@@ -37,9 +37,9 @@ typedef (HTMLScriptElement or SVGScriptElement) HTMLOrSVGScriptElement;
 // FIXME: Document should have a constructor. crbug.com/238234
 interface Document : Node {
     [SameObject] readonly attribute DOMImplementation implementation;
-    readonly attribute DOMString URL;
+    [ImplementedAs=urlForBinding] readonly attribute DOMString URL;
     // FIXME: documentURI should not be nullable.
-    [ImplementedAs=url] readonly attribute DOMString? documentURI;
+    [ImplementedAs=urlForBinding] readonly attribute DOMString? documentURI;
     [MeasureAs=DocumentOrigin] readonly attribute DOMString origin;
     [RuntimeEnabled=suborigins] readonly attribute DOMString suborigin;
     readonly attribute DOMString compatMode;