RFR (XS) JDK-8015272: Make @Contended within the same group to use the same oop map

[Aleksey Shipilev]

Hi,

Please review the simple improvement:
  http://cr.openjdk.java.net/~shade/8015272/webrev.00/

I have copy-pasted the same block from the non- at Contended handling,
because it is generic for both cases. The change is also on the path
which is excercized only with @Contended with the same tag. Both
@Contended regression tests cover this case, as well as j.l.Thread
containing @Contended over the TLR state implicitly tests it in every VM
run.

Testing:
 - Linux x86_64 fastdebug/release: all hotspot/test/runtime jtreg
 - JPRT full cycle against hotspot-rt
 - vm.quick (running)

-Aleksey.