headless: Replace headless::Maybe with base::Optional

headless/lib/browser/types_cc.template

Index: headless/lib/browser/types_cc.template
diff --git a/headless/lib/browser/types_cc.template b/headless/lib/browser/types_cc.template
index 1c2d6b81462b47bfa1334ecc5ad25040fbe9a50c..5be72cf79240a5f5be27e902a802b040a4ada3ff 100644
--- a/headless/lib/browser/types_cc.template
+++ b/headless/lib/browser/types_cc.template
@@ -83,7 +83,7 @@ std::unique_ptr<{{type.id}}> {{type.id}}::Parse(const base::Value& value, ErrorR
   if (object->Get("{{property.name}}", &{{value_name}})) {
     errors->SetName("{{property.name}}");
       {% if property.optional %}
-    result->{{property.name | camelcase_to_hacker_style}}_ = Just(internal::FromValue<{{resolve_type(property).raw_type}}>::Parse(*{{value_name}}, errors));
+    result->{{property.name | camelcase_to_hacker_style}}_ = internal::FromValue<{{resolve_type(property).raw_type}}>::Parse(*{{value_name}}, errors);
       {% else %}
     result->{{property.name | camelcase_to_hacker_style}}_ = internal::FromValue<{{resolve_type(property).raw_type}}>::Parse(*{{value_name}}, errors);
       {% endif %}
@@ -107,8 +107,8 @@ std::unique_ptr<base::Value> {{type.id}}::Serialize() const {
     {% for property in type.properties %}
       {% set type = resolve_type(property) %}
       {% if property.optional %}
-  if ({{property.name | camelcase_to_hacker_style}}_.IsJust())
-    result->Set("{{property.name}}", internal::ToValue({{type.to_raw_type % ("%s_.FromJust()" % property.name | camelcase_to_hacker_style)}}));
+  if ({{property.name | camelcase_to_hacker_style}}_)
+    result->Set("{{property.name}}", internal::ToValue({{type.to_raw_type % ("%s_.value()" % property.name | camelcase_to_hacker_style)}}));
       {% else %}
   result->Set("{{property.name}}", internal::ToValue({{type.to_raw_type % ("%s_" % property.name | camelcase_to_hacker_style)}}));
       {% endif %}