Fix incorrect initial dex cache size.

We were previously setting it to be sizeof(DexCacheClass) instead
of sizeof(DexCache). This was causing some problems with
compaction when I relied on the object sizes being accurate to
visit objects in the bump pointer space.

Bug: 8981901
Change-Id: Iede04763aced041986b1b239368fc867143ad70d
diff --git a/runtime/mirror/class-inl.h b/runtime/mirror/class-inl.h
index 88cffb7..cd5e865 100644
--- a/runtime/mirror/class-inl.h
+++ b/runtime/mirror/class-inl.h
@@ -35,9 +35,7 @@
 inline size_t Class::GetObjectSize() const {
   DCHECK(!IsVariableSize()) << " class=" << PrettyTypeOf(this);
   DCHECK_EQ(sizeof(size_t), sizeof(int32_t));
-  size_t result = GetField32(OFFSET_OF_OBJECT_MEMBER(Class, object_size_), false);
-  DCHECK_GE(result, sizeof(Object)) << " class=" << PrettyTypeOf(this);
-  return result;
+  return GetField32(OFFSET_OF_OBJECT_MEMBER(Class, object_size_), false);
 }
 
 inline Class* Class::GetSuperClass() const {