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

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

 {#---
   Macro for enum definition, and the declaration of associated functions.
   `is_static` is relevant if this enum declaration is defined within a class, in
   which case associated functions need to be static.
 ---#}
 {%- macro enum_decl(enum, is_static=false) %}
-enum {{enum.name}} : int32_t {
+enum class {{enum.name}} : int32_t {
 {%- for field in enum.fields %}
 {%-    if field.value %}
-  {{enum.name|to_all_caps}}_{{field.name}} = {{field.value|expression_to_text}},
+  {{field.name}} = {{field.value|expression_to_text}},
 {%-    else %}
-  {{enum.name|to_all_caps}}_{{field.name}},
+  {{field.name}},
 {%-    endif %}
 {%- endfor %}
 };
 {{is_valid_enum_decl(enum, is_static)}}
 {%- endmacro %}
 
 {#--- macros for the declaration & definitions of enum-associated functions.
       Namely:
   * {enum_name}_IsValidValue:  returns true if the given enum has a valid value
                                for this generated version of enum.
@@ skipping 14 matching lines @@
 {{enum.name}}_IsValidValue({{enum.name}} value) {
   switch (static_cast<int32_t>(value)) {
 {%- for enum_field in enum.fields|groupby('numeric_value') %}
     case {{enum_field[0]}}:
 {%- endfor %}
       return true;
   }
   return false;
 }
 {%- endmacro %}
+
+{%- macro global_enum_operators_decl(enum, class_name = '') %}
+{% if class_name != '' -%}
+std::ostream& operator<<(std::ostream& stream,
+                         const {{class_name}}::{{enum.name}}& val);
+{%- else -%}
+std::ostream& operator<<(std::ostream& stream, const {{enum.name}}& val);
+{%- endif -%}
+{%- endmacro %}
+
+{%- macro global_enum_operators_def(enum, class_name = '') %}
+{% if class_name != '' -%}
+std::ostream& operator<<(std::ostream& stream,
+                         const {{class_name}}::{{enum.name}}& val) {
+  return (stream << static_cast<int32_t>(val));
+}
+{%- else -%}
+std::ostream& operator<<(std::ostream& stream, const {{enum.name}}& val) {
+  return (stream << static_cast<int32_t>(val));
+}
+{%- endif -%}
+{%- endmacro %}