Make the mark stack expandable for the CC collector.

Bug: 12687968
Change-Id: I5d05df5524f54c6adb964901e5a963eb042cb2e1
diff --git a/runtime/gc/collector/concurrent_copying.h b/runtime/gc/collector/concurrent_copying.h
index 8efad73..c32b19e 100644
--- a/runtime/gc/collector/concurrent_copying.h
+++ b/runtime/gc/collector/concurrent_copying.h
@@ -182,6 +182,7 @@
   void ReenableWeakRefAccess(Thread* self) SHARED_REQUIRES(Locks::mutator_lock_);
   void DisableMarking() SHARED_REQUIRES(Locks::mutator_lock_);
   void IssueDisableMarkingCheckpoint() SHARED_REQUIRES(Locks::mutator_lock_);
+  void ExpandGcMarkStack() SHARED_REQUIRES(Locks::mutator_lock_);
 
   space::RegionSpace* region_space_;      // The underlying region space.
   std::unique_ptr<Barrier> gc_barrier_;