Enable GVN for polymorphic loads by not expanding them at the HIR level.

src/hydrogen.h

Index: src/hydrogen.h
===================================================================
--- src/hydrogen.h	(revision 7299)
+++ src/hydrogen.h	(working copy)
@@ -794,10 +794,6 @@
 
   void HandlePropertyAssignment(Assignment* expr);
   void HandleCompoundAssignment(Assignment* expr);
-  void HandlePolymorphicLoadNamedField(Property* expr,
-                                       HValue* object,
-                                       ZoneMapList* types,
-                                       Handle<String> name);
   void HandlePolymorphicStoreNamedField(Assignment* expr,
                                         HValue* object,
                                         HValue* value,