Fixing overrideMimeType on IE10.

tests/html/xhr_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library XHRTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_individual_config.dart';
 import 'dart:async';
 import 'dart:html';
 import 'dart:json' as json;
@@ skipping 33 matching lines @@
       expect(HttpRequest.supportsProgressEvent, isTrue);
     });
   });
 
   group('supported_onLoadEnd', () {
     test('supported', () {
       expect(HttpRequest.supportsLoadEndEvent, isTrue);
     });
   });
 
+  group('supported_overrideMimeType', () {
+    test('supported', () {
+      expect(HttpRequest.supportsOverrideMimeType, isTrue);
+    });
+  });
+
   group('xhr', () {
     test('XHR No file', () {
       HttpRequest xhr = new HttpRequest();
       xhr.open("GET", "NonExistingFile", async: true);
       xhr.onReadyStateChange.listen(expectAsyncUntil1((event) {
         if (xhr.readyState == HttpRequest.DONE) {
           validate404(xhr);
         }
       }, () => xhr.readyState == HttpRequest.DONE));
       xhr.send();
@@ skipping 75 matching lines @@
       HttpRequest.getString('NonExistingFile').then(
         (_) { fail('Succeeded for non-existing file.'); },
         onError: expectAsync1((error) {
           validate404(error.target);
         }));
     });
 
     test('XHR.request responseType arraybuffer', () {
       if (Platform.supportsTypedData) {
         HttpRequest.request(url, responseType: 'arraybuffer',
-          mimeType: 'application/binary',
           requestHeaders: {'Content-Type': 'text/xml'}).then(
           expectAsync1((xhr) {
             expect(xhr.status, equals(200));
             var byteBuffer = xhr.response;
             expect(byteBuffer, new isInstanceOf<ByteBuffer>());
             expect(byteBuffer, isNotNull);
           }));
       }
     });
 
     test('HttpRequestProgressEvent', () {
       var expectation = HttpRequestProgressEvent.supported ?
           returnsNormally : throws;
       expect(() {
         var event = new Event.eventType('XMLHttpRequestProgressEvent', '');
         expect(event is HttpRequestProgressEvent, isTrue);
       }, expectation);
     });
+
+    test('overrideMimeType', () {
+      var expectation =
+          HttpRequest.supportsOverrideMimeType ? returnsNormally : throws;
+
+      expect(() {
+        HttpRequest.request(url, mimeType: 'application/binary');
+      }, expectation);
+    });
   });
 
   group('xhr_requestBlob', () {
     test('XHR.request responseType blob', () {
       if (Platform.supportsTypedData) {
         return HttpRequest.request(url, responseType: 'blob').then(
           (xhr) {
             expect(xhr.status, equals(200));
             var blob = xhr.response;
             expect(blob is Blob, isTrue);
             expect(blob, isNotNull);
           });
       }
     });
   });
 }