Fix escaped index JSON parsing

test/mjsunit/regress/regress-json-parse-index.js

Index: test/mjsunit/regress/regress-json-parse-index.js
diff --git a/test/mjsunit/regress/regress-crbug-351262.js b/test/mjsunit/regress/regress-json-parse-index.js
similarity index 72%
copy from test/mjsunit/regress/regress-crbug-351262.js
copy to test/mjsunit/regress/regress-json-parse-index.js
index a2f4eadc0de5c2bd7d27f6e78ff9940fce7b0f85..d1a785aaf1ef35714d5702be15cff74bfaa73521 100644
--- a/test/mjsunit/regress/regress-crbug-351262.js
+++ b/test/mjsunit/regress/regress-json-parse-index.js
@@ -2,5 +2,5 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-for (var x in this) {};
-JSON.stringify(this);
+var o = JSON.parse('{"\\u0030":100}');
+assertEquals(100, o[0]);