[es6] conditionally ignore TDZ semantics for formals

src/scopes.h

Index: src/scopes.h
diff --git a/src/scopes.h b/src/scopes.h
index 021b7b3b17820a8aae3da5aa20096c846d7f056d..f2ba050c7b997731a3d434d06a81fe0b38ffca8d 100644
--- a/src/scopes.h
+++ b/src/scopes.h
@@ -403,6 +403,8 @@ class Scope: public ZoneObject {
     return has_simple_parameters_;
   }
 
+  bool has_parameter_expressions() const { return has_parameter_expressions_; }
+
   // TODO(caitp): manage this state in a better way. PreParser must be able to
   // communicate that the scope is non-simple, without allocating any parameters
   // as the Parser does. This is necessary to ensure that TC39's proposed early
@@ -419,6 +421,16 @@ class Scope: public ZoneObject {
     return !scope->is_function_scope() || scope->has_simple_parameters();
   }
 
+  void SetHasParameterExpressions() {
+    DCHECK(is_function_scope());
+    has_parameter_expressions_ = true;
+  }
+
+  bool HasParameterExpressions() {
+    Scope* scope = ClosureScope();
+    return !scope->is_function_scope() || scope->has_parameter_expressions();
+  }
+
   // The local variable 'arguments' if we need to allocate it; NULL otherwise.
   Variable* arguments() const {
     DCHECK(!is_arrow_scope() || arguments_ == nullptr);
@@ -661,6 +673,7 @@ class Scope: public ZoneObject {
   // Info about the parameter list of a function.
   int arity_;
   bool has_simple_parameters_;
+  bool has_parameter_expressions_;
   Variable* rest_parameter_;
   int rest_index_;