7032531: G1: enhance GC logging to include more accurate eden / survivor size transitions

This changeset extends the logging information generated by +PrintGCDetails to also print out separate size transitions for the eden, survivors, and old regions.

Reviewed-by: ysr, brutisso

hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp

@@ -3456,6 +3456,8 @@ G1CollectedHeap::do_collection_pause_at_safepoint(double target_pause_time_ms) {
           }
         }
       }
+      // We have to do this after we decide whether to expand the heap or not.
+      g1_policy()->print_heap_transition();
 
       if (mark_in_progress()) {
         concurrent_mark()->update_g1_committed();