Makes it so mojom files don't need a module

mojo/public/bindings/generators/cpp_templates/module-internal.h.tmpl

 // Copyright 2013 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.
 
 {%- set header_guard = "%s_INTERNAL_H_"|
         format(module.path|upper|replace("/","_")|replace(".","_")) %}
 
 #ifndef {{header_guard}}
 #define {{header_guard}}
 
 #include "mojo/public/cpp/bindings/lib/bindings_internal.h"
 {%- for import in imports %}
 #include "{{import.module.path}}-internal.h"
 {%- endfor %}
 
+{%- if namespace %}
 namespace {{namespace}} {
+{%- endif %}
 
 {#--- Wrapper forward declarations #}
 {%  for struct in structs %}
 class {{struct.name}};
 {%- endfor %}
 
 namespace internal {
 
 #pragma pack(push, 1)
 
 {#--- Class declarations #}
 {%  for struct in structs %}
 {%    include "struct_declaration.tmpl" %}
 {%- endfor %}
 
 #pragma pack(pop)
 
 }  // namespace internal
+{%- if namespace %}
 }  // namespace {{namespace}}
+{%- endif %}
 
 #endif  // {{header_guard}}