[es6] Fix scoping for default parameters in arrow functions

src/parameter-initializer-rewriter.h

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_PARAMETER_EXPRESSION_REWRITER_H_
+#define V8_PARAMETER_EXPRESSION_REWRITER_H_
+
+#include "src/ast.h"
+
+namespace v8 {
+namespace internal {
+
+
+void RewriteParameterInitializerScope(uintptr_t stack_limit,
+                                      Expression* initializer, Scope* old_scope,
+                                      Scope* new_scope);
+
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_PARAMETER_EXPRESSION_REWRITER_H_