Implement DOMImplementation::createDocumentType

Implementation according to spec:
http://dom.spec.whatwg.org/#dom-domimplementation-createdocumenttype

Closes #1489.

src/components/script/dom/bindings/codegen/DOMImplementation.webidl

@@ -14,9 +14,9 @@
 interface DOMImplementation {
   /*boolean hasFeature(DOMString feature,
                      [TreatNullAs=EmptyString] DOMString version);*/
-  /*[Throws]
+  [Creator, Throws]
   DocumentType createDocumentType(DOMString qualifiedName, DOMString publicId,
-                                  DOMString systemId);*/
+                                  DOMString systemId);
   /*[Throws]
   Document createDocument(DOMString? namespace,
                           [TreatNullAs=EmptyString] DOMString qualifiedName,

src/components/script/dom/domimplementation.rs

@@ -3,7 +3,11 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use dom::bindings::codegen::DOMImplementationBinding;
-use dom::bindings::utils::{Reflector, Reflectable, reflect_dom_object};
+use dom::bindings::utils::{DOMString, Reflector, Reflectable, reflect_dom_object};
+use dom::bindings::utils::{Fallible, InvalidCharacter, NamespaceError};
+use dom::bindings::utils::{QName, Name, InvalidXMLName, xml_name_type};
+use dom::documenttype::DocumentType;
+use dom::node::AbstractNode;
 use dom::window::Window;
 
 pub struct DOMImplementation {
@@ -34,3 +38,20 @@ impl Reflectable for DOMImplementation {
         &mut self.reflector_
     }
 }
+
+// http://dom.spec.whatwg.org/#domimplementation
+impl DOMImplementation {
+    // http://dom.spec.whatwg.org/#dom-domimplementation-createdocumenttype
+    pub fn CreateDocumentType(&self, qname: DOMString, pubid: DOMString, sysid: DOMString) -> Fallible<AbstractNode> {
+        // FIXME: To be removed in https://github.com/mozilla/servo/issues/1498
+        let force_quirks : bool = false;
+        match xml_name_type(qname) {
+            // Step 1.
+            InvalidXMLName => Err(InvalidCharacter),
+            // Step 2.
+            Name => Err(NamespaceError),
+            // Step 3.
+            QName => Ok(DocumentType::new(qname, Some(pubid), Some(sysid), force_quirks, self.owner.Document()))
+        }
+    }
+}

src/test/html/content/test_document_implementation.html

@@ -11,6 +11,17 @@
                 is(document.implementation, implementation, "test1-2, basic test");
             }
 
+            // test2: createDocumentType
+            {
+                is(document.doctype, null, "test2-0, createDocumentType");
+
+                var doctype = document.implementation.createDocumentType("html", null, null);
+                is_a(doctype && doctype, DocumentType, "test2-1, createDocumentType");
+
+                doctype = document.implementation.createDocumentType("html:html", null, null);
+                is_a(doctype && doctype, DocumentType, "test2-2, createDocumentType");
+            }
+
             finish();
         </script>
     </head>