Implement two-argument check inline cache.

vm/ic_data.cc

 // 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.
 
 #include "vm/ic_data.h"
 #include "vm/object.h"
 
 namespace dart {
 
 // ICData is a ValueObject, therefore 'data' need not be a ZoneObject.
@@ skipping 73 matching lines @@
 void ICData::SetCheckAt(intptr_t index,
                         const GrowableArray<const Class*>& classes,
                         const Function& target) {
   ASSERT(!data_->IsNull());
   ASSERT((0 <= index) && (index < NumberOfChecks()));
   intptr_t pos = kChecksStartIndex + ArrayElementsPerCheck() * index;
   ASSERT(classes.length() == NumberOfArgumentsChecked());
   for (intptr_t i = 0; i < classes.length(); i++) {
     // Null is used as terminating object, do not add it.
     ASSERT(!classes[i]->IsNull());
-    // Contract says that the class of null (NullClass) cannot be added.
-    ASSERT(!classes[i]->IsNullClass());
     data_->SetAt(pos++, *(classes[i]));
   }
   ASSERT(!target.IsNull());
   data_->SetAt(pos, target);
 }
 
 
 void ICData::GetOneClassCheckAt(intptr_t index,
                                 Class* cls,
                                 Function* target) const {
@@ skipping 17 matching lines @@
   intptr_t pos = 1 + 1 + ArrayElementsPerCheck() * index;
   for (intptr_t i = 0; i < NumberOfArgumentsChecked(); i++) {
     Class& cls = Class::ZoneHandle();
     cls ^= data_->At(pos++);
     classes->Add(&cls);
   }
   (*target) ^= data_->At(pos);
 }
 
 }  // namespace dart