mojo/common: Decouple GURL dependency

mojo/common/url_type_converters.cc

+// 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.
+
+#include "mojo/common/url_type_converters.h"
+
+#include "url/gurl.h"
+
+namespace mojo {
+
+String TypeConverter<String, GURL>::Convert(const GURL& input) {
+  return String(input.spec());
+}
+
+GURL TypeConverter<GURL, String>::Convert(const String& input) {
+  return GURL(input.get());
+}
+
+}  // namespace mojo