[crankshaft] Properly handle OOB string accesses.

test/mjsunit/regress/regress-crbug-665793.js

Index: test/mjsunit/regress/regress-crbug-665793.js
diff --git a/test/mjsunit/regress/regress-crbug-665793.js b/test/mjsunit/regress/regress-crbug-665793.js
new file mode 100644
index 0000000000000000000000000000000000000000..d445d5194e83e5a0bbc5f85cbec374f195178248
--- /dev/null
+++ b/test/mjsunit/regress/regress-crbug-665793.js
@@ -0,0 +1,12 @@
+// 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.
+
+// Flags: --allow-natives-syntax
+
+function foo() {
+  return 'x'[1];
+}
+assertEquals(undefined, foo());
+%OptimizeFunctionOnNextCall(foo);
+assertEquals(undefined, foo());