[mojo] Support native types with mojom wire format

mojo/public/interfaces/bindings/tests/chromium_test.typemap

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 {
   "c++": {
     "mojo.test.PickledStruct": {
       "typename": "mojo::test::PickledStructChromium",
       "headers": [
         "mojo/public/cpp/bindings/tests/pickled_struct_chromium.h"
       ]
+    },
+    "mojo.test.Rect": {
+      "typename": "mojo::test::RectChromium",
+      "headers": [
+        "mojo/public/cpp/bindings/tests/rect_chromium.h"
+      ]
     }
   }
 }