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

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

 {% from "enum_macros.tmpl" import enum_decl -%}
 class {{struct.name}} {
  public:
   using Data_ = internal::{{struct.name}}_Data;
 
 {#--- Enums #}
 {%- for enum in struct.enums -%}
   {{enum_decl(enum, is_static=true)|indent(2)}}
 {%- endfor %}
 
@@ skipping 26 matching lines @@
 {%- endif %}
   bool Equals(const {{struct.name}}& other) const;
 
 {#--- Struct members #}
 {%  for field in struct.fields %}
 {%-   set type = field.kind|cpp_wrapper_type %}
 {%-   set name = field.name %}
   {{type}} {{name}};
 {%- endfor %}
 };
+
+{#--- Enum Operators #}
+{% from "enum_macros.tmpl" import global_enum_operators_decl -%}
+{%- for enum in struct.enums %}
+  {{global_enum_operators_decl(enum, class_name=struct.name)}}
+{%- endfor %}