Adjusted HttpRequest documentation to discourage using open and send in simple cases.

tools/dom/docs/docs.json

 {
   "dart.dom.html": {
     "CanvasGradient": {
       "comment": [
         "/**",
         " * An opaque canvas object representing a gradient.",
         " *",
         " * Created by calling [createLinearGradient] or [createRadialGradient] on a",
         " * [CanvasRenderingContext2D] object.",
         " *",
@@ skipping 341 matching lines @@
         "open": [
           "/**",
           "   * Specify the desired `url`, and `method` to use in making the request.",
           "   *",
           "   * 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",
+          "   * 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 [common MIME types](http://en.wikipedia.org/wiki/Internet_media_type#List_of_common_media_types)",
           "   */"
@@ skipping 64 matching lines @@
           "   *",
           "   * The response is processed as",
           "   * `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",
+          "   * finer-grained control is needed.",
+          "   *",
           "   * See also:",
           "   *",
           "   *   * [send](https://developer.mozilla.org/en-US/docs/DOM/XMLHttpRequest#send%28%29)",
           "   * from MDN.",
           "   */"
         ],
         "status": [
           "/**",
           "   * The http result code from the request (200, 404, etc).",
           "   * See also: [Http Status Codes](http://en.wikipedia.org/wiki/List_of_HTTP_status_codes)",
@@ skipping 79 matching lines @@
           "   *",
           "   * [oldVersion] should match the database's current [version] exactly.",
           "   *",
           "   * * [Database.changeVersion](http://www.w3.org/TR/webdatabase/#dom-database-changeversion) from W3C.",
           "   */"
         ]
       }
     }
   }
 }