Add mojo struct traits for GURL so that it can be sent over mojoms.

url/mojo/gurl.typemap

 // Copyright 2016 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.
 
-#include "ui/views/run_all_unittests.h"
-
-int MasterProcessMain(int argc, char** argv) {
-  return views::RunAllUnittests(argc, argv);
+{
+  "c++": {
+    "url.mojom.Url": {
+      "typename": "GURL",
+      "headers": [
+        "url/mojo/url_gurl_struct_traits.h"
+      ]
+    }
+  }
 }