Adding HttpRequest method to make it easier to post form data.

tools/dom/templates/html/impl/impl_XMLHttpRequest.darttemplate

 // 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.
 
 part of $LIBRARYNAME;
 
 /**
  * A utility for retrieving data from a URL.
  *
  * HttpRequest can be used to obtain data from http, ftp, and file
@@ skipping 34 matching lines @@
    *
    * * [request]
    */
   static Future<String> getString(String url,
       {bool withCredentials, void onProgress(ProgressEvent e)}) {
     return request(url, withCredentials: withCredentials,
         onProgress: onProgress).then((xhr) => xhr.responseText);
   }
 
   /**
+   * Makes a server POST request with the specified data encoded as form data.
+   *
+   * This is similar to sending a FormData object with broader browser
+   * support but limited to string values.
+   *
+   * See also:
+   *
+   * * [request]
+   */
+  static Future<HttpRequest> postFormData(String url, Map<String, String> data,
+      {bool withCredentials, String responseType,
+      Map<String, String> requestHeaders,
+      void onProgress(ProgressEvent e)}) {
+
+    var parts = [];
+    data.forEach((key, value) {
+      parts.add('${Uri.encodeQueryComponent(key)}='
+          '${Uri.encodeQueryComponent(value)}');
+    });
+    var formData = parts.join('&');
+
+    if (requestHeaders == null) {
+      requestHeaders = <String, String>{};
+    }
+    requestHeaders.putIfAbsent('Content-Type',
+        () => 'application/x-www-form-urlencoded; charset=UTF-8');
+
+    return request(url, method: 'POST', withCredentials: withCredentials,
+        responseType: responseType,
+        requestHeaders: requestHeaders, sendData: formData,
+        onProgress: onProgress);
+  }
+
+  /**
    * Creates a URL request for the specified [url].
    *
    * By default this will do an HTTP GET request, this can be overridden with
    * [method].
    *
    * The Future is completed when the response is available.
    *
    * The [withCredentials] parameter specified that credentials such as a cookie
    * (already) set in the header or
    * [authorization headers](http://tools.ietf.org/html/rfc1945#section-10.2)
@@ skipping 117 matching lines @@
 $if DART2JS
     var xhr = new HttpRequest();
     return JS('bool', '("overrideMimeType" in #)', xhr);
 $else
     return true;
 $endif
   }
 
 $!MEMBERS
 }