Can now correctly add documentation to constructors.

tools/dom/docs/docs.json

 {
   "html": {
     "CanvasGradient": {
       "comment": [
         "/**",
         " * An opaque canvas object representing a gradient.",
         " *",
         " * Created by calling [createLinearGradient] or [createRadialGradient] on a",
         " * [CanvasRenderingContext2D] object.",
         " *",
@@ skipping 192 matching lines @@
           "   *",
           "   * * [HTMLCanvasElement](https://developer.mozilla.org/en-US/docs/DOM/HTMLCanvasElement) from MDN.",
           "   *",
           "   * * [toDataUrl](http://dev.w3.org/html5/spec/the-canvas-element.html#dom-canvas-todataurl) from W3C.",
           "   */"
         ],
         "width": [
           "/// The width of this canvas element in CSS pixels."
         ]
       }
+    },
+    "XMLHttpRequest": {
+      "members": {
+        "XMLHttpRequest": [
+          "/**",
+          "   * General constructor for any type of request (GET, POST, etc).",
+          "   *",
+          "   * This call is used in conjunction with [open]:",
+          "   *",
+          "   *     var request = new HttpRequest();",
+          "   *     request.open('GET', 'http://dartlang.org')",
+          "   *     request.on.load.add((event) => print('Request complete'));",
+          "   *",
+          "   * is the (more verbose) equivalent of",
+          "   *",
+          "   *     var request = new HttpRequest.get('http://dartlang.org', (event) => print('Request complete'));",
+          "   */"
+        ]
+      }
     }
   }
-}
+}