Be more vigilant with deferred loading.

runtime/vm/object.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 10497 matching lines @@
 RawClass* LibraryPrefix::LookupClass(const String& class_name) const {
   const Object& obj = Object::Handle(LookupObject(class_name));
   if (obj.IsClass()) {
     return Class::Cast(obj).raw();
   }
   return Class::null();
 }
 
 
 void LibraryPrefix::set_is_loaded() const {
+  Isolate::Current()->IncrPrefixInvalidationGen();
   StoreNonPointer(&raw_ptr()->is_loaded_, true);
 }
 
 
 bool LibraryPrefix::LoadLibrary() const {
   // Non-deferred prefixes are loaded.
   ASSERT(is_deferred_load() || is_loaded());
   if (is_loaded()) {
     return true;  // Load request has already completed.
   }
@@ skipping 11212 matching lines @@
   return UserTag::null();
 }
 
 
 const char* UserTag::ToCString() const {
   const String& tag_label = String::Handle(label());
   return tag_label.ToCString();
 }
 
 }  // namespace dart