Avoid unnecessarily clearing/resetting region_space_ for each GC.

Bug: 12687968
Test: test-art-host with CC.
Change-Id: Idf8e6753ba9de23866e15634a093b47ae6a5c239
diff --git a/runtime/gc/heap.cc b/runtime/gc/heap.cc
index 3b9abd2..1bb84fc 100644
--- a/runtime/gc/heap.cc
+++ b/runtime/gc/heap.cc
@@ -612,6 +612,8 @@
       concurrent_copying_collector_ = new collector::ConcurrentCopying(this,
                                                                        "",
                                                                        measure_gc_performance);
+      DCHECK(region_space_ != nullptr);
+      concurrent_copying_collector_->SetRegionSpace(region_space_);
       garbage_collectors_.push_back(concurrent_copying_collector_);
     }
     if (MayUseCollector(kCollectorTypeMC)) {
@@ -2708,7 +2710,6 @@
         collector = semi_space_collector_;
         break;
       case kCollectorTypeCC:
-        concurrent_copying_collector_->SetRegionSpace(region_space_);
         collector = concurrent_copying_collector_;
         break;
       case kCollectorTypeMC: