Implement two-argument check inline cache.

vm/ic_data.h

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 // Class for handling inline cache stubs
 
 // The caller of an instance function passes the IC-data array in a specific
 // register (ECX on ia32).
 // That array contains information relevant for the call site: function name and
 // inline cache data. Class ICData is a wrapper around that array.
 // The array format is:
 // 0: function-name
 // 1: N, number of arguments checked.
 // 2 .. (length - 1): group of checks, each check containing:
 //   - N classes.
 //   - 1 target function.
 // Whenever first N arguments of an instance call have the same class as the
 // check, jump to the target function.
 // Array is null terminated (all classes and target are null objects).
-// The array does not contain Null-Classes. Null objects cannot be added.
+// The array may contain Null-Classes. Null objects cannot be added.
 
 #ifndef VM_IC_DATA_H_
 #define VM_IC_DATA_H_
 
 #include "vm/allocation.h"
 #include "vm/growable_array.h"
 
 namespace dart {
 
 class Array;
@@ skipping 42 matching lines @@
 
   const Array* data_;
 
 
   DISALLOW_COPY_AND_ASSIGN(ICData);
 };
 
 }  // namespace dart
 
 #endif  // VM_IC_DATA_H_