Refactor large object sweeping.

Moved basic sweeping logic into large_object_space.cc.
Renamed SpaceSetMap -> ObjectSet.

Change-Id: I938c1f29f69b0682350347da2bd5de021c0e0224
diff --git a/runtime/gc/heap.h b/runtime/gc/heap.h
index 622850f..cc4d7be 100644
--- a/runtime/gc/heap.h
+++ b/runtime/gc/heap.h
@@ -54,7 +54,7 @@
 namespace accounting {
   class HeapBitmap;
   class ModUnionTable;
-  class SpaceSetMap;
+  class ObjectSet;
 }  // namespace accounting
 
 namespace collector {
@@ -468,7 +468,7 @@
 
   // Mark all the objects in the allocation stack in the specified bitmap.
   void MarkAllocStack(accounting::SpaceBitmap* bitmap1, accounting::SpaceBitmap* bitmap2,
-                      accounting::SpaceSetMap* large_objects, accounting::ObjectStack* stack)
+                      accounting::ObjectSet* large_objects, accounting::ObjectStack* stack)
       EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_);
 
   // Mark the specified allocation stack as live.