Parser: Fix InitializerRewriter.

test/mjsunit/regress/regress-679727.js

Index: test/mjsunit/regress/regress-679727.js
diff --git a/test/mjsunit/regress/regress-679727.js b/test/mjsunit/regress/regress-679727.js
new file mode 100644
index 0000000000000000000000000000000000000000..40931ca39cc3540635c6869617300efb770c805d
--- /dev/null
+++ b/test/mjsunit/regress/regress-679727.js
@@ -0,0 +1,6 @@
+// Copyright 2017 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.
+
+f = (e=({} = {} = 1)) => {}; f(1);
+((e = ({} = {} = {})) => {})(1)