Convert Class::descriptor_ from StringPiece to String (as part of image loading)

Change-Id: Iab5ffa353661a7c06ee79af1f40d399a53777174
diff --git a/src/heap.h b/src/heap.h
index 99f6554..0cf0b57 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -62,6 +62,7 @@
 
   static void RecordAllocation(Space* space, const Object* object);
   static void RecordFree(Space* space, const Object* object);
+  static void RecordImageAllocations(Space* space);
 
   static void CollectGarbageInternal();