Converted document object attributes type to USVString as per specification

https://html.spec.whatwg.org/multipage/dom.html#documents

With this CL, |domain| and |referrer| that includes unpaired surrogate codepoint are replaced
by \uFFFD. Since in case of both DOMString and USVString, same exception ("Uncaught SecurityError:
Failed to set the 'domain' property on 'Document': 'text is �' could not be parsed properly.")
is thrown, so no test is added.

Bug: 
Change-Id: Ie01fdc71fd9a540f2df4a71ff8cafbd205fe96ef
Reviewed-on: https://chromium-review.googlesource.com/795592
Commit-Queue: Bhagirathi Satpathy <bhagirathi.s@samsung.com>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521323}

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

@@ -94,8 +94,8 @@ typedef (HTMLScriptElement or SVGScriptElement) HTMLOrSVGScriptElement;
     // resource metadata management
 
     [PutForwards=href, Unforgeable] readonly attribute Location? location;
-    [RaisesException=Setter] attribute DOMString domain;
-    readonly attribute DOMString referrer;
+    [RaisesException=Setter] attribute USVString domain;
+    readonly attribute USVString referrer;
     [RaisesException, RuntimeCallStatsCounter=DocumentCookie] attribute DOMString cookie;
     readonly attribute DOMString lastModified;
     readonly attribute DocumentReadyState readyState;