RFR: overflow integer during size calculation

[Zhengyu Gu]

Hi,

Found in QA TCK test, we overflowed int when calculating size in bytes.


Webrev: 
http://cr.openjdk.java.net/~zgu/shenandoah/size-calc-ovreflow/webrev.00/

Test:
   tier3_gc_shenandoah

Thanks,

-Zhengyu