Cpp bindings: add typedef for callbacks.

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

 
 class {{struct.name}} {
  public:
-  typedef internal::{{struct.name}}_Data Data_;
+  using Data_ = internal::{{struct.name}}_Data;
 
 {#--- Constants #}
 {%- for constant in struct.constants %}
   static const {{constant.kind|cpp_pod_type}} {{constant.name}};
 {%- endfor %}
 {#--- Enums #}
 {%- for enum in struct.enums -%}
 {%    macro enum_def() %}{% include "enum_declaration.tmpl" %}{% endmacro %}
   {{enum_def()|indent(2)}}
 {%- endfor %}
@@ skipping 17 matching lines @@
 {%- endif %}
   bool Equals(const {{struct.name}}& other) const;
 
 {#--- Getters #}
 {%  for field in struct.fields %}
 {%-   set type = field.kind|cpp_wrapper_type %}
 {%-   set name = field.name %}
   {{type}} {{name}};
 {%- endfor %}
 };