Refactor large object sweeping.

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

Change-Id: I938c1f29f69b0682350347da2bd5de021c0e0224
diff --git a/runtime/gc/accounting/space_bitmap.cc b/runtime/gc/accounting/space_bitmap.cc
index 52c02f7..99800fc 100644
--- a/runtime/gc/accounting/space_bitmap.cc
+++ b/runtime/gc/accounting/space_bitmap.cc
@@ -44,7 +44,7 @@
                       reinterpret_cast<void*>(HeapLimit()));
 }
 
-void SpaceSetMap::Walk(SpaceBitmap::Callback* callback, void* arg) {
+void ObjectSet::Walk(SpaceBitmap::Callback* callback, void* arg) {
   for (const mirror::Object* obj : contained_) {
     callback(const_cast<mirror::Object*>(obj), arg);
   }
@@ -267,18 +267,6 @@
   }
 }
 
-std::string SpaceSetMap::GetName() const {
-  return name_;
-}
-
-void SpaceSetMap::SetName(const std::string& name) {
-  name_ = name;
-}
-
-void SpaceSetMap::CopyFrom(const SpaceSetMap& space_set) {
-  contained_ = space_set.contained_;
-}
-
 std::ostream& operator << (std::ostream& stream, const SpaceBitmap& bitmap) {
   return stream
     << bitmap.GetName() << "["