Fix polymorphic keyed load handler selection for string elements

test/mjsunit/regress/regress-crbug-594955.js

Index: test/mjsunit/regress/regress-crbug-594955.js
diff --git a/test/mjsunit/regress/regress-crbug-594955.js b/test/mjsunit/regress/regress-crbug-594955.js
new file mode 100644
index 0000000000000000000000000000000000000000..69db053f4a4f8db2fe81907406aee3caac20b65b
--- /dev/null
+++ b/test/mjsunit/regress/regress-crbug-594955.js
@@ -0,0 +1,11 @@
+// Copyright 2016 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.
+
+function g(s, key) { return s[key]; }
+
+assertEquals(g(new String("a"), "length"), 1);
+assertEquals(g(new String("a"), "length"), 1);
+assertEquals(g("a", 32), undefined);
+assertEquals(g("a", "length"), 1);
+assertEquals(g(new String("a"), "length"), 1);