In generated code for ia32 don't load object's class directly from class_ field.

runtime/vm/isolate.h

 // 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.
 
 #ifndef VM_ISOLATE_H_
 #define VM_ISOLATE_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/class_table.h"
@@ skipping 43 matching lines @@
                            bool visit_prologue_weak_persistent_handles,
                            bool validate_frames);
 
   // Visits weak object pointers.
   void VisitWeakPersistentHandles(HandleVisitor* visit,
                                   bool visit_prologue_weak_persistent_handles);
 
   StoreBufferBlock* store_buffer() { return &store_buffer_; }
 
   ClassTable* class_table() { return &class_table_; }
+  static intptr_t class_table_offset() {
+    return OFFSET_OF(Isolate, class_table_);
+  }
 
   Dart_MessageNotifyCallback message_notify_callback() const {
     return message_notify_callback_;
   }
   void set_message_notify_callback(Dart_MessageNotifyCallback value) {
     message_notify_callback_ = value;
   }
 
   const char* name() const { return name_; }
 
@@ skipping 219 matching lines @@
   Isolate* new_isolate_;
   Isolate* saved_isolate_;
   uword saved_stack_limit_;
 
   DISALLOW_COPY_AND_ASSIGN(SwitchIsolateScope);
 };
 
 }  // namespace dart
 
 #endif  // VM_ISOLATE_H_