RFR(S) 8038412: Move object_iterate_careful down from Space to ContigousSpace and CFLSpace

[Mikael Gerdin]

Hi,

I'm doing some cleanups in the "Space" classes to simplify the code for the G1 
class unloading work[1].
Here's a change to move code only used for CMS from virtuals on Space to only 
be declared and defined where needed.

Bug: https://bugs.openjdk.java.net/browse/JDK-8038412
Webrev:  http://cr.openjdk.java.net/~mgerdin/8038412/webrev.0

/Mikael

[1] http://openjdk.java.net/jeps/156