Make so that array length property access uses a new IC that tracks the array map.

src/objects-inl.h

 // 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:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3477 matching lines @@
   return kind >= FIRST_IC_KIND && kind <= LAST_IC_KIND;
 }
 
 
 Code::Flags Code::ComputeFlags(Kind kind,
                                InlineCacheState ic_state,
                                ExtraICState extra_ic_state,
                                StubType type,
                                int argc,
                                InlineCacheHolderFlag holder) {
-  // Extra IC state is only allowed for call IC stubs or for store IC
-  // stubs.
+  // Extra IC state is only allowed for call IC stubs, store IC stubs or
+  // load ICs with type CALLBACKS.
   ASSERT(extra_ic_state == kNoExtraICState ||
          kind == CALL_IC ||
          kind == STORE_IC ||
-         kind == KEYED_STORE_IC);
+         kind == KEYED_STORE_IC ||
+         (kind == LOAD_IC && type == CALLBACKS));
   // Compute the bit mask.
   int bits = KindField::encode(kind)
       | ICStateField::encode(ic_state)
       | TypeField::encode(type)
       | ExtraICStateField::encode(extra_ic_state)
       | (argc << kArgumentsCountShift)
       | CacheHolderField::encode(holder);
   return static_cast<Flags>(bits);
 }
 
@@ skipping 2027 matching lines @@
 #undef WRITE_UINT32_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_