Cpp bindings: add typedef for callbacks.

mojo/public/tools/bindings/generators/cpp_templates/interface_declaration.tmpl

 {%- import "interface_macros.tmpl" as interface_macros %}
 class {{interface.name}}Proxy;
 class {{interface.name}}Stub;
 
 class {{interface.name}}RequestValidator;
 {%- if interface|has_callbacks %}
 class {{interface.name}}ResponseValidator;
 {%- endif %}
 {% if interface.client %}
 class {{interface.client}};
@@ skipping 26 matching lines @@
 {#--- Enums #}
 {%- for enum in interface.enums %}
 {%    macro enum_def() %}{% include "enum_declaration.tmpl" %}{% endmacro %}
   {{enum_def()|indent(2)}}
 {%- endfor %}
 
 {#--- Methods #}
   virtual ~{{interface.name}}() {}
 
 {%- for method in interface.methods %}
+{%    if method.response_parameters != None %}
+  typedef {{interface_macros.declare_callback(method)}} {{method.name}}Callback;

[jamesr, 2015/01/28 17:25:32]

can you use the 'using' syntax instead? i.e.

using {{method.name}}Callback = {{interface_macros...}};

that's what our style guide recommends and marginally easier to parse for humans
(imo) since the name of the type alias is at the beginning instead of buried at
the end

[yzshen1, 2015/01/28 18:30:43]

Done.

+{%-   endif %}
   virtual void {{method.name}}({{interface_macros.declare_request_params("", method)}}) = 0;
 {%- endfor %}
 };