[es6] implement default/optional parameters (WIP / comments)

src/variables.cc

Index: src/variables.cc
diff --git a/src/variables.cc b/src/variables.cc
index c0b8bd784353aa0ad349689b30ce7578de80e116..859ed95977eff103c3057c79bfdeae9585d36b49 100644
--- a/src/variables.cc
+++ b/src/variables.cc
@@ -49,7 +49,8 @@ Variable::Variable(Scope* scope, const AstRawString* name, VariableMode mode,
       force_context_allocation_(false),
       is_used_(false),
       initialization_flag_(initialization_flag),
-      maybe_assigned_(maybe_assigned_flag) {
+      maybe_assigned_(maybe_assigned_flag),
+      parameter_kind_(ParameterKind::NonParameter) {
   // Var declared variables never need initialization.
   DCHECK(!(mode == VAR && initialization_flag == kNeedsInitialization));
 }