For c++, Generate enum classes instead of enum from mojom.

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

 {%- import "interface_macros.tmpl" as interface_macros %}
 {%- import "struct_macros.tmpl" as struct_macros %}
 {%- from "enum_macros.tmpl" import is_valid_enum_def %}
+{%- from "enum_macros.tmpl" import global_enum_operators_def %}
 
 {%- set class_name = interface.name %}
 {%- set proxy_name = interface.name ~ "Proxy" %}
 {%- set namespace_as_string = "%s"|format(namespace|replace(".","::")) %}
 
 {%- macro alloc_params(struct) %}
 {%-   for param in struct.packed.packed_fields_in_ordinal_order %}
   {{param.field.kind|cpp_result_type}} p_{{param.field.name}} {};
 {%-   endfor %}
   {{struct_macros.deserialize(struct, "params", "p_%s")}}
@@ skipping 23 matching lines @@
 {%-  for constant in interface.constants %}
 {%-   if constant.kind|is_integral_kind %}
 MOJO_STATIC_CONST_MEMBER_DEFINITION const {{constant.kind|cpp_pod_type}} {{interface.name}}::{{constant.name}};
 {%-   else %}
 MOJO_STATIC_CONST_MEMBER_DEFINITION const {{constant.kind|cpp_pod_type}} {{interface.name}}::{{constant.name}} = {{constant|constant_value}};
 {%-   endif %}
 {%- endfor %}
 
 {#--- Enums #}
 {%- for enum in interface.enums %}
-  {{is_valid_enum_def(enum, class_name=interface.name)|indent(2)}}
+  {{is_valid_enum_def(enum, class_name=interface.name)}}
+  {{global_enum_operators_def(enum, class_name=interface.name)}}
 {%- endfor %}
 
 {#--- ForwardToCallback definition #}
 {%- for method in interface.methods -%}
 {%-   if method.response_parameters != None %}
 class {{class_name}}_{{method.name}}_ForwardToCallback
     : public mojo::MessageReceiver {
  public:
   {{class_name}}_{{method.name}}_ForwardToCallback(
       const {{class_name}}::{{method.name}}Callback& callback)
@@ skipping 255 matching lines @@
     default:
       break;
   }
 
   // Unrecognized message.
   ReportValidationError(
       mojo::internal::VALIDATION_ERROR_MESSAGE_HEADER_UNKNOWN_METHOD);
   return false;
 }
 {%- endif -%}