Reapply changes to Expando patching.

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index 71ee7af2c506276dc321607fc4537c2638b326be..02ad757616b4d1f2be098e0527b341e7b3337238 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -666,12 +666,6 @@ RawError* Object::Init(Isolate* isolate) {
   RegisterClass(cls, name, core_impl_lib);
   pending_classes.Add(cls, Heap::kOld);
 
-  cls = Class::New<WeakProperty>();
-  object_store->set_weak_property_class(cls);
-  name = Symbols::_WeakProperty();
-  RegisterPrivateClass(cls, name, core_impl_lib);
-  pending_classes.Add(cls, Heap::kOld);
-
   // Initialize the base interfaces used by the core VM classes.
   const Script& script = Script::Handle(Bootstrap::LoadCoreScript(false));
 
@@ -789,6 +783,11 @@ RawError* Object::Init(Isolate* isolate) {
   name = Symbols::_ExternalFloat64Array();
   RegisterPrivateClass(cls, name, core_lib);
 
+  cls = Class::New<WeakProperty>();
+  object_store->set_weak_property_class(cls);
+  name = Symbols::_WeakProperty();
+  RegisterPrivateClass(cls, name, core_lib);
+
   // Set the super type of class Stacktrace to Object type so that the
   // 'toString' method is implemented.
   cls = object_store->stacktrace_class();