Fix the tests after my previous commit.

sky/engine/bindings/scripts/templates/interface_dart.template

Index: sky/engine/bindings/scripts/templates/interface_dart.template
diff --git a/sky/engine/bindings/scripts/templates/interface_dart.template b/sky/engine/bindings/scripts/templates/interface_dart.template
index 274760a300be6de8a44112430c0b05b7fdc23dd6..a69850a21a66f233f971ecf86e4a04faf2857b76 100644
--- a/sky/engine/bindings/scripts/templates/interface_dart.template
+++ b/sky/engine/bindings/scripts/templates/interface_dart.template
@@ -11,7 +11,7 @@ part of sky.core;
         {{ '{' if arg.is_named else '[' }}
         {%- endif -%}
         {{ arg.dart_type }} {{ arg.name }}
-        {%- if arg.is_optional %} = {{ arg.dart_default_value }}
+        {%- if arg.is_optional %} {{ ':' if arg.is_named else '='}}  {{ arg.dart_default_value }}
         {#- TODO(eseidel): This does not support having both optional and named arguments! -#}
         {%- if loop.last -%}{{ '}' if arg.is_named else ']' }}{%- endif -%}
         {%- endif -%}