Fixed 6895456: Eliminate dependency on java.io.ObjectStreamClass during boot
Webrev at: http://cr.openjdk.java.net/~mchung/6895456/webrev.00/java.io.ObjectStreamClass is not needed if not doing serialization. Move getSignatureClass static method to java.io.ObjectStreamField class. ObjectStreamField is always loaded due to the declaration of serialPersistentFields in a few core classes as they have evolved in the previous releases.
Thanks Mandy
