RFR (S): 8189797:Fix initializer lists in G1ConcurrentMark and G1CMTask

[Thomas Schatzl]

Hi all,

  can I have quick reviews for this change that fixes initializer lists
for the aforementioned classes?

It just rearranges their members so they reflect the actual
initialization order as mandated by the c++ standard. This is just
nicer for anyone trying to think about initialization order. There is
no actual bug fixed.

CR:
https://bugs.openjdk.java.net/browse/JDK-8189797
Webrev:
http://cr.openjdk.java.net/~tschatzl/8189797/webrev/
Testing:
local compilation

Thanks,
  Thomas