Forbid setting responseType on all sync XHRs.

LayoutTests/fast/html/imports/import-defaultView.html

Index: LayoutTests/fast/html/imports/import-defaultView.html
diff --git a/LayoutTests/fast/html/imports/import-defaultView.html b/LayoutTests/fast/html/imports/import-defaultView.html
index 4c133ca870a0f6ddea4ac2f355b26b722539ea14..7b9b0f52c71cecfad9b9234f0bb23cea6ef5e878 100644
--- a/LayoutTests/fast/html/imports/import-defaultView.html
+++ b/LayoutTests/fast/html/imports/import-defaultView.html
@@ -8,14 +8,19 @@
 <script>
 shouldBe("importLink.import.defaultView", "document.defaultView");
 
+window.jsTestIsAsync = true;
+
 var xhr = new XMLHttpRequest();
-xhr.open("GET", "resources/root.html", false);
+xhr.open("GET", "resources/root.html", true);
 xhr.responseType = "document";
-xhr.send();
-shouldBeNull("xhr.response.defaultView");
+xhr.onload = function() {
+  shouldBeNull("xhr.response.defaultView");
 
-createdDoc = document.implementation.createHTMLDocument("Hello");
-shouldBeNull("createdDoc.defaultView");
+  createdDoc = document.implementation.createHTMLDocument("Hello");
+  shouldBeNull("createdDoc.defaultView");
+  finishJSTest();
+};
+xhr.send();
 
 </script>
 </body>