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

runtime/vm/assembler_ia32.h

Index: runtime/vm/assembler_ia32.h
diff --git a/runtime/vm/assembler_ia32.h b/runtime/vm/assembler_ia32.h
index 1cb69eccc3ae2796b2e5192d6cefa27f87cd2fac..8bcb37342e9de3d01a734fb74628e2746248f363 100644
--- a/runtime/vm/assembler_ia32.h
+++ b/runtime/vm/assembler_ia32.h
@@ -529,6 +529,17 @@ class Assembler : public ValueObject {
   void CallRuntime(const RuntimeEntry& entry);
 
   /*
+   * Loading and comparing classes of objects
+   */
+  void LoadClassOfObject(Register result, Register object, Register scratch);
+
+  void LoadClassIndexOfObject(Register result, Register object);
+
+  void CompareClassOfObject(Register object,
+                            const Class& clazz,
+                            Register scratch);
+
+  /*
    * Misc. functionality
    */
   void SmiTag(Register reg) {