RFR (XXS): 8189665: Change id parameter of G1ConcurrentMark::task() to uint

[Thomas Schatzl]

Hi all,

  can I get reviews for this cleanup change that changes the type of
the "id" parameter of the mentioned method from int to uint?

It only ever gets passed worker_id's (or 0's) which have been uints for
a long time now.

CR:
https://bugs.openjdk.java.net/browse/JDK-8189665
Webrev:
http://cr.openjdk.java.net/~tschatzl/8189665/webrev/
Testing:
local compilation, jprt

Thanks,
  Thomas