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

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index 6fdbd2046be7dfff7f5dbb795bde7f8f64c90cc2..8f44597eca6a6292234e4847077daff691af7084 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -61,6 +61,9 @@ class Isolate : public BaseIsolate {
   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_;