RFR: 9+8u: BrooksPointer::(word|byte)_size should be uint

[Aleksey Shipilev]

Hi,

BrooksPointer::(word|byte)_size are now implemented as size_t, which makes
compilers think they overflow int expressions. We know these are small values,
so we can declare them to be uint. New asserts are added to check the are indeed
positive. A few places around their uses fixed too.

Fix:
  http://cr.openjdk.java.net/~shade/shenandoah/brooks-uints/webrev.01/

Same thing goes to 8u.

Testing: hotspot_gc_shenandoah on 9 and 8u.

Thanks,
-Aleksey