Pref service: expose all read-only PrefStores through Mojo

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

 {#---
   Macro for enum definition, and the declaration of associated functions.
 ---#}
 
 {%- macro enum_decl(enum) %}
 {%-   set enum_name = enum|get_name_for_kind(flatten_nested_kind=True) %}
 enum class {{enum_name}} : int32_t {
 {%-   for field in enum.fields %}
 {%-     if field.value %}
   {{field.name}} = {{field.value|expression_to_text}},
@@ skipping 60 matching lines @@
 };
 {%- endmacro %}
 
 {%- macro enum_hash(enum) %}
 {%-   set enum_name = enum|get_qualified_name_for_kind(
           flatten_nested_kind=True) %}
 template <>
 struct hash<{{enum_name}}>
     : public mojo::internal::EnumHashImpl<{{enum_name}}> {};
 {%- endmacro %}
+
+{%- macro enum_hash_blink(enum) %}
+{%-   set enum_name = enum|get_qualified_name_for_kind(
+          flatten_nested_kind=True, include_variant=False) %}
+{%-   set hash_fn_name = enum|get_name_for_kind ~ "HashFn" %}
+{%-   set empty_value = -1000 %}
+{%-   set deleted_value = -1001 %}
+namespace WTF {
+struct {{hash_fn_name}} {
+  static unsigned hash(const {{enum_name}}& value) {
+    return 0;  // TODO(tibell): Implement.
+  }
+  static bool equal(const {{enum_name}}& left, const {{enum_name}}& right) {
+    return left == right;
+  }
+  static const bool safeToCompareToEmptyOrDeleted = true;
+};
+
+template <>
+struct DefaultHash<{{enum_name}}> {
+  using Hash = {{hash_fn_name}};
+};
+
+template <>
+struct HashTraits<{{enum_name}}>
+    : public GenericHashTraits<{{enum_name}}> {
+  static const bool hasIsEmptyValueFunction = true;
+  static bool isEmptyValue(const {{enum_name}}& value) {
+    return value == static_cast<{{enum_name}}>({{empty_value}});
+  }
+  static void constructDeletedValue({{enum_name}}& slot, bool) {
+    slot = static_cast<{{enum_name}}>({{deleted_value}});
+  }
+  static bool isDeletedValue(const {{enum_name}}& value) {
+    return value == static_cast<{{enum_name}}>({{deleted_value}});
+  }
+};
+}  // namespace WTF
+{%- endmacro %}