Mojo: Add support for constants to the IDL compiler.

mojo/public/tools/bindings/generators/cpp_templates/module.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_H_"|
         format(module.path|upper|replace("/","_")|replace(".","_")) %}
 
 #ifndef {{header_guard}}
 #define {{header_guard}}
 
 #include "mojo/public/cpp/bindings/array.h"
 #include "mojo/public/cpp/bindings/callback.h"
 #include "mojo/public/cpp/bindings/interface.h"
 #include "{{module.path}}-internal.h"
 {%- for import in imports %}
 #include "{{import.module.path}}.h"
 {%- endfor %}
 
 {%- for namespace in namespaces_as_array %}
 namespace {{namespace}} {
 {%- endfor %}
 
+{#--- Constants #}
+{%  for constant in module.constants %}
+extern const {{constant.kind|cpp_pod_type}} {{constant.name}};
+{%- endfor %}
+
 {#--- Enums #}
 {%  for enum in enums %}
 {%    include "enum_declaration.tmpl" %}
 {%- endfor %}
 
 {#--- Interface Forward Declarations -#}
 {%  for interface in interfaces %}
 class {{interface.name}};
 // A typesafe variant of MessagePipeHandle:
 typedef mojo::Interface<{{interface.name}}>::Handle {{interface.name}}Handle;
@@ skipping 30 matching lines @@
 namespace mojo {
 namespace internal {
 {%    for enum in enums %}
 {%      include "enum_traits.tmpl" %}
 {%-   endfor %}
 }  // namespace internal
 }  // namespace mojo
 {%- endif %}
 
 #endif  // {{header_guard}}