Move mojo::internal::MessageBuilder out of the |internal| namespace.

mojo/public/cpp/bindings/tests/BUILD.gn

 # Copyright 2014 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.
 
 import("../../../mojo_application.gni")
 import("../../../mojo_sdk.gni")
 
 mojo_sdk_source_set("tests") {
   testonly = true
 
   sources = [
     "array_unittest.cc",
     "binding_callback_unittest.cc",
     "binding_unittest.cc",
     "bounds_checker_unittest.cc",
     "buffer_unittest.cc",
     "callback_unittest.cc",
     "connector_unittest.cc",
     "constant_unittest.cc",
     "container_test_util.cc",
     "equals_unittest.cc",
     "handle_passing_unittest.cc",
     "interface_ptr_unittest.cc",
     "interface_unittest.cc",
     "iterator_test_util.h",
     "iterator_util_unittest.cc",
     "map_unittest.cc",
+    "message_builder_unittest.cc",
     "message_queue.cc",
     "message_queue.h",
     "request_response_unittest.cc",
     "router_unittest.cc",
     "sample_service_unittest.cc",
     "serialization_api_unittest.cc",
     "serialization_warning_unittest.cc",
     "string_unittest.cc",
     "struct_unittest.cc",
     "type_conversion_unittest.cc",
@@ skipping 93 matching lines @@
   ]
 
   mojo_sdk_deps = [
     "mojo/public/cpp/application:standalone",
     "mojo/public/cpp/application:test_support_standalone",
     "mojo/public/cpp/bindings",
     "mojo/public/cpp/system",
     "mojo/public/interfaces/bindings/tests:versioning_test_client_interfaces",
   ]
 }