Address comments about safely casting handles.

runtime/vm/object.cc

Index: runtime/vm/object.cc
===================================================================
--- runtime/vm/object.cc	(revision 17701)
+++ runtime/vm/object.cc	(working copy)
@@ -9316,14 +9316,28 @@
 
 RawClass* Type::type_class() const {
   ASSERT(HasResolvedTypeClass());
+#ifdef DEBUG
+  Class& type_class = Class::Handle();
+  type_class ^= raw_ptr()->type_class_;
+  return type_class.raw();
+#else
   return reinterpret_cast<RawClass*>(raw_ptr()->type_class_);
+#endif
 }
 
 
 RawUnresolvedClass* Type::unresolved_class() const {
+  ASSERT(!HasResolvedTypeClass());
+#ifdef DEBUG
+  UnresolvedClass& unresolved_class = UnresolvedClass::Handle();
+  unresolved_class ^= raw_ptr()->type_class_;
+  ASSERT(!unresolved_class.IsNull());
+  return unresolved_class.raw();
+#else
   ASSERT(!Object::Handle(raw_ptr()->type_class_).IsNull());
   ASSERT(Object::Handle(raw_ptr()->type_class_).IsUnresolvedClass());
   return reinterpret_cast<RawUnresolvedClass*>(raw_ptr()->type_class_);
+#endif
 }