RFR [8]: Revert accidental G1 closure rename

[Aleksey Shipilev]

Hi,

Looking through webrevs, I noticed we have accidentally renamed one of G1 closures in 8u:

$ hg diff
diff -r dbf4a74655c8 src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp
--- a/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp	Tue Aug 15 10:30:16 2017 -0400
+++ b/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp	Mon Aug 21 09:27:13 2017 +0200
@@ -2604,10 +2604,10 @@

 // Calls a SpaceClosure on a HeapRegion.

-class ShenandoahSpaceClosureRegionClosure: public HeapRegionClosure {
+class SpaceClosureRegionClosure: public HeapRegionClosure {
   SpaceClosure* _cl;
 public:
-  ShenandoahSpaceClosureRegionClosure(SpaceClosure* cl) : _cl(cl) {}
+  SpaceClosureRegionClosure(SpaceClosure* cl) : _cl(cl) {}
   bool doHeapRegion(HeapRegion* r) {
     _cl->do_space(r);
     return false;
@@ -2615,7 +2615,7 @@
 };

 void G1CollectedHeap::space_iterate(SpaceClosure* cl) {
-  ShenandoahSpaceClosureRegionClosure blk(cl);
+  SpaceClosureRegionClosure blk(cl);
   heap_region_iterate(&blk);
 }

This happened because there is a double definition of SpaceClosureRegionClosure, once in G1, and
once in Shenandoah. After rename, the Shenandoah version has "Shenandoah" prefix, future-proofing
subsequent changes.

Thanks,
-Aleksey