Make supported-xml-content-types.html tests faster.

LayoutTests/http/tests/xmlhttprequest/resources/supported-xml-content-types.js

+function getXMLOfType(testcase)
+{
+    var request = new XMLHttpRequest();
+    function failure()
+    {
+        testFailed(testcase.xmlType)
+        runNextTest();
+    }
+    function checkResult()
+    {
+        var statusText = "";
+        if (request.responseXML) {
+            var typeElement = request.responseXML.firstChild;
+            if (testcase.expectPass && typeElement) {
+                if (typeElement.textContent !== testcase.xmlType)
+                    statusText = "Incorrect content: " + typeElement.textContent;
+            } else {
+                statusText = "Document type: " + request.getResponseHeader("Content-type");
+            }
+        } else if (testcase.expectPass) {
+            statusText = "Response type: " + request.getResponseHeader("Content-type");
+        }
+        if (statusText)
+            testFailed(testcase.xmlType + " -- " + statusText + "; responseXML: " + new XMLSerializer().serializeToString(request.responseXML));
+        else
+            testPassed(testcase.xmlType);
+
+        runNextTest();
+    }
+
+    var escapedType = escape(testcase.xmlType).replace(/\+/g, "^^PLUS^^"); // Perl CGI module seems replace + with a space
+    request.open("GET", "supported-xml-content-types.cgi?type=" + escapedType, true);
+    request.onerror = checkResult;
+    request.onload = checkResult;
+    request.send(null);
+}
+
+var tests = [];
+
+function testXMLType(type, expected)
+{
+    tests.push({xmlType: type, expectPass: expected});
+}
+
+function runNextTest()
+{
+    if (tests.length)
+        getXMLOfType(tests.shift());
+    else
+        finishJSTest();
+}