Sync the DOMParser interface with spec

Source/core/xml/DOMParser.idl

 /*
  * Copyright (C) 2006 Apple Computer, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
+// https://dvcs.w3.org/hg/innerhtml/raw-file/tip/index.html#the-domparser-interface
+
+enum SupportedType {
+    "text/html",
+    "text/xml",
+    "application/xml",
+    "application/xhtml+xml",
+    "image/svg+xml"
+};
+
 [
+    Constructor,
+    TypeChecking=Interface,

[Jens Widell, 2015/01/16 15:10:45]

[TypeChecking=Interface] will have no effect since there are no interface type
arguments to any method in the interface.

Conversion to string can't fail, and enums are always checked.

[philipj_slow, 2015/01/16 19:20:07]

Ah, I was assuming things without testing. I'll revert this bit.

     WillBeGarbageCollected,
-    Constructor
 ] interface DOMParser {
-    [RaisesException] Document parseFromString([Default=Undefined] optional DOMString str,
-                             [Default=Undefined] optional DOMString contentType);
+    Document parseFromString(DOMString str, SupportedType type);
 };