Mojo C++ bindings: add a new mode to generator to use native STL/WTF types

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

 {%- macro declare_params(prefix, parameters) %}
 {%-   for param in parameters -%}
 {{param.kind|cpp_wrapper_param_type}} {{prefix}}{{param.name}}
 {%- if not loop.last %}, {% endif %}
 {%-   endfor %}
 {%- endmacro %}
 
-{%- macro declare_responder_params(prefix, parameters, for_blink) %}
+{%- macro declare_responder_params(prefix, parameters, for_blink, use_new_wrapper_types) %}
 {%-   for param in parameters -%}
-{%-     if (not param.kind|is_string_kind) or for_blink -%}
+{%-     if (not param.kind|is_string_kind) or for_blink or
+           use_new_wrapper_types -%}
 {{param.kind|cpp_wrapper_param_type}} {{prefix}}{{param.name}}
 {%-     else %}
 mojo::String {{prefix}}{{param.name}}
 {%-     endif %}
 {%- if not loop.last %}, {% endif %}
 {%-   endfor %}
 {%- endmacro %}
 
-{%- macro declare_callback(method, for_blink) -%}
+{%- macro declare_callback(method, for_blink, use_new_wrapper_types) -%}
 base::Callback<void(
 {%-   for param in method.response_parameters -%}
 {#- TODO(yzshen): For historical reasons, we use mojo::String here (instead of
     const mojo::String&) inconsistently. Preserve the behavior temporarily. #}
-{%- if (not param.kind|is_string_kind) or for_blink -%}
+{%-     if (not param.kind|is_string_kind) or for_blink or
+           use_new_wrapper_types -%}
 {{param.kind|cpp_wrapper_param_type}}
-{%- else -%}
+{%-     else -%}
 mojo::String
-{%- endif %}
-{%- if not loop.last %}, {% endif %}
+{%-     endif %}
+{%-     if not loop.last %}, {% endif %}
 {%-   endfor -%}
 )>
 {%- endmacro -%}
 
 {%- macro declare_request_params(prefix, method) -%}
 {{declare_params(prefix, method.parameters)}}
 {%-   if method.response_parameters != None -%}
 {%- if method.parameters %}, {% endif -%}
 const {{method.name}}Callback& callback
 {%-   endif -%}
 {%- endmacro -%}
 
 {%- macro declare_sync_method_params(prefix, method) -%}
 {{declare_params(prefix, method.parameters)}}
 {%-   if method.response_parameters %}
 {%-     if method.parameters %}, {% endif %}
 {%-     for param in method.response_parameters -%}
 {{param.kind|cpp_wrapper_type}}* {{prefix}}{{param.name}}
 {%-       if not loop.last %}, {% endif %}
 {%-     endfor %}
 {%-   endif -%}
 {%- endmacro -%}