[es6] Fix scoping for default parameters in arrow functions

src/ast-expression-visitor.h

Index: src/ast-expression-visitor.h
diff --git a/src/ast-expression-visitor.h b/src/ast-expression-visitor.h
index 80bfa221717d544ef7c8e11d4613ad80c953dc03..d9a4fc823863d527fd6aaa8ba3f642e5eeb75774 100644
--- a/src/ast-expression-visitor.h
+++ b/src/ast-expression-visitor.h
@@ -21,7 +21,8 @@ namespace internal {
 
 class AstExpressionVisitor : public AstVisitor {
  public:
-  AstExpressionVisitor(Isolate* isolate, FunctionLiteral* root);
+  AstExpressionVisitor(Isolate* isolate, Expression* root);
+  AstExpressionVisitor(uintptr_t stack_limit, Expression* root);
   void Run();
 
  protected:
@@ -38,7 +39,7 @@ class AstExpressionVisitor : public AstVisitor {
   AST_NODE_LIST(DECLARE_VISIT)
 #undef DECLARE_VISIT
 
-  FunctionLiteral* root_;
+  Expression* root_;
   int depth_;
 
   DISALLOW_COPY_AND_ASSIGN(AstExpressionVisitor);