Flatten the string in StringToDouble function.

test/mjsunit/regress/regress-425551.js

Index: test/mjsunit/regress/regress-425551.js
diff --git a/test/mjsunit/deserialize-reference.js b/test/mjsunit/regress/regress-425551.js
similarity index 58%
copy from test/mjsunit/deserialize-reference.js
copy to test/mjsunit/regress/regress-425551.js
index b03201315932eab59e38c135d219192e6dcdf0eb..eee5e32f04e3107d4c13f410382b7d5bef2bddd8 100644
--- a/test/mjsunit/deserialize-reference.js
+++ b/test/mjsunit/regress/regress-425551.js
@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --cache=code --serialize-toplevel
-
-var a = "123";
-assertEquals(a, "123");
+var array = new Int8Array(10);
+array[/\u007d\u00fc\u0043/] = 1.499
+assertEquals(1.499, array[/\u007d\u00fc\u0043/]);