Adding ability to specify request headers and mime type for Future-based XHRs.

sdk/lib/html/dart2js/html_dart2js.dart

 /// The Dart HTML library.
 library dart.dom.html;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:_collection-dev' hide Symbol;
 import 'dart:html_common';
 import 'dart:indexed_db';
 import 'dart:isolate';
 import 'dart:json' as json;
@@ skipping 10555 matching lines @@
    * * If `Access-Control-Expose-Headers` has not been set to true, only a subset of all the response headers will be returned when calling [getAllRequestHeaders].
    *
    * Note that requests for file:// URIs are only supported by Chrome extensions
    * with appropriate permissions in their manifest. Requests to file:// URIs
    * will also never fail- the Future will always complete successfully, even
    * when the file cannot be found.
    *
    * See also: [authorization headers](http://en.wikipedia.org/wiki/Basic_access_authentication).
    */
   static Future<HttpRequest> request(String url,
-      {String method, bool withCredentials, String responseType, sendData,
+      {String method, bool withCredentials, String responseType,
+      String mimeType, Map<String, String> requestHeaders, sendData,
       void onProgress(ProgressEvent e)}) {
     var completer = new Completer<HttpRequest>();
 
     var xhr = new HttpRequest();
     if (method == null) {
       method = 'GET';
     }
     xhr.open(method, url, async: true);
 
     if (withCredentials != null) {
       xhr.withCredentials = withCredentials;
     }
 
     if (responseType != null) {
       xhr.responseType = responseType;
     }
 
+    if (mimeType != null) {
+      xhr.overrideMimeType(mimeType);
+    }
+
+    if (requestHeaders != null) {
+      requestHeaders.forEach((header, value) {
+        xhr.setRequestHeader(header, value);
+      });
+    }
+
     if (onProgress != null) {
       xhr.onProgress.listen(onProgress);
     }
 
     xhr.onLoad.listen((e) {
       // Note: file:// URIs have status of 0.
       if ((xhr.status >= 200 && xhr.status < 300) ||
           xhr.status == 0 || xhr.status == 304) {
         completer.complete(xhr);
       } else {
@@ skipping 16331 matching lines @@
       _position = nextPosition;
       return true;
     }
     _current = null;
     _position = _array.length;
     return false;
   }
 
   T get current => _current;
 }