Codereview request for 6898310: (cs) Charset cache lookups should be synchronized

[Xueming Shen]

Hi,

This is a forward porting. Same fix has been in jdk5/6, and will be in 
jdk 7u2 later.

http://cr.openjdk.java.net/~sherman/6898310/webrev

The change itself is relative simple. And given its race-condition 
nature, no reliable
regression test case is provided.

Thanks!

-Sherman