Make sure transitioned arrays efficiently call builtin Array functions

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index 97a98017c5897e6bedb38d6d54ac751acf04bd89..ffee3761ef036f81c4b724b8f0598f397c1f8440 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -1,4 +1,4 @@
-// Copyright 2011 the V8 project authors. All rights reserved.
+// Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
@@ -889,13 +889,15 @@ class MacroAssembler: public Assembler {
                                    XMMRegister xmm_scratch,
                                    Label* fail);
 
-  // Check if the map of an object is equal to a specified map and
-  // branch to label if not. Skip the smi check if not required
-  // (object is known to be a heap object)
+  // Check if the map of an object is equal to a specified map and branch to
+  // label if not. Skip the smi check if not required (object is known to be a
+  // heap object). If mode is ALLOW_ELEMENT_TRANSITION_MAPS, then also match
+  // against maps that are ElementsKind transition maps of the specificed map.
   void CheckMap(Register obj,
                 Handle<Map> map,
                 Label* fail,
-                SmiCheckType smi_check_type);
+                SmiCheckType smi_check_type,
+                MapCheckMode mode = REQUIRE_EXACT_MAP);
 
   // Check if the map of an object is equal to a specified map and branch to a
   // specified target if equal. Skip the smi check if not required (object is