Add zone task support to http-requests.

tools/dom/docs/docs.json

 {
   "dart.dom.html": {
     "AbstractWorker": {
       "members": {
         "errorEvent": [
           "/**",
           "   * Static factory designed to expose `error` events to event",
           "   * handlers that are not necessarily instances of [AbstractWorker].",
           "   *",
           "   * See [EventStreamProvider] for usage information.",
@@ skipping 4183 matching lines @@
           "   *",
           "   * By default the request is done asyncronously, with no user or password",
           "   * authentication information. If `async` is false, the request will be send",
           "   * synchronously.",
           "   *",
           "   * Calling `open` again on a currently active request is equivalent to",
           "   * calling `abort`.",
           "   *",
           "   * Note: Most simple HTTP requests can be accomplished using the [getString],",
           "   * [request], [requestCrossOrigin], or [postFormData] methods. Use of this",
-          "   * `open` method is intended only for more complext HTTP requests where",
+          "   * `open` method is intended only for more complex HTTP requests where",
           "   * finer-grained control is needed.",
           "   */"
         ],
         "overrideMimeType": [
           "/**",
           "   * Specify a particular MIME type (such as `text/xml`) desired for the",
           "   * response.",
           "   *",
           "   * This value must be set before the request has been sent. See also the list",
           "   * of [IANA Official MIME types](https://www.iana.org/assignments/media-types/media-types.xhtml)",
@@ skipping 76 matching lines @@
           "   * `text/xml` stream, unless responseType = 'document' and the request is",
           "   * synchronous.",
           "   */"
         ],
         "send": [
           "/**",
           "   * Send the request with any given `data`.",
           "   *",
           "   * Note: Most simple HTTP requests can be accomplished using the [getString],",
           "   * [request], [requestCrossOrigin], or [postFormData] methods. Use of this",
-          "   * `send` method is intended only for more complext HTTP requests where",
+          "   * `send` method is intended only for more complex HTTP requests where",
           "   * finer-grained control is needed.",
           "   *",
           "   * ## Other resources",
           "   *",
           "   * * [XMLHttpRequest.send](https://developer.mozilla.org/en-US/docs/DOM/XMLHttpRequest#send%28%29)",
           "   *   from MDN.",
           "   */"
         ],
         "setRequestHeader": [
           "/**",
@@ skipping 888 matching lines @@
           "   *",
           "   * See also:",
           "   *",
           "   * * [Database.changeVersion](http://www.w3.org/TR/webdatabase/#dom-database-changeversion) from W3C.",
           "   */"
         ]
       }
     }
   }
 }