RFR(xxs): 8150648: Re-enable TestPLABResize.java after JDK-8150183 is fixed

[Michail Chernov]

Hi

Could I have a review for this small change which returns quarantined 
test back, please?

Bug: https://bugs.openjdk.java.net/browse/JDK-8150648
Webrev: http://cr.openjdk.java.net/~mchernov/8150648/webrev.00/

I will need a sponsor.

Thanks
Michail