Move mirror::Object setters to ObjPtr

Bug: 31113334

Test: test-art-host

Change-Id: I2c4c84645e194c3c435a4a6fd670176b0e98671f
diff --git a/runtime/globals.h b/runtime/globals.h
index 28534e4..6164225 100644
--- a/runtime/globals.h
+++ b/runtime/globals.h
@@ -172,6 +172,9 @@
 static constexpr bool kIsVdexEnabled = false;
 #endif
 
+// Size of a heap reference.
+static constexpr size_t kHeapReferenceSize = sizeof(uint32_t);
+
 }  // namespace art
 
 #endif  // ART_RUNTIME_GLOBALS_H_