dart2js cps: A few extra RTI optimizations.

pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart

 // Copyright (c) 2013, 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.
 library dart2js.ir_nodes;
 
 import 'dart:collection';
 import 'cps_fragment.dart' show CpsFragment;
 import 'cps_ir_nodes_sexpr.dart';
 import '../constants/values.dart' as values;
 import '../dart_types.dart' show DartType, InterfaceType, TypeVariableType;
@@ skipping 1416 matching lines @@
 
   /// Initial values for the fields on the class.
   /// The order corresponds to the order of fields on the class.
   final List<Reference<Primitive>> argumentRefs;
 
   /// The runtime type information structure which contains the type arguments.
   ///
   /// May be `null` to indicate that no type information is needed because the
   /// compiler determined that the type information for instances of this class
   /// is not needed at runtime.
-  final Reference<Primitive> typeInformationRef;
+  Reference<Primitive> typeInformationRef;
 
   final SourceInformation sourceInformation;
 
   Primitive argument(int n) => argumentRefs[n].definition;
   Iterable<Primitive> get arguments => _dereferenceList(argumentRefs);
   Primitive get typeInformation => typeInformationRef?.definition;
 
   CreateInstance(this.classElement, List<Primitive> arguments,
       Primitive typeInformation, this.sourceInformation)
       : this.argumentRefs = _referenceList(arguments),
@@ skipping 1662 matching lines @@
     plug(new Branch.loose(
         _definitions.getCopy(node.conditionRef),
         _copies[node.trueContinuation],
         _copies[node.falseContinuation])..isStrictCheck = node.isStrictCheck);
   }
 
   visitUnreachable(Unreachable node) {
     plug(new Unreachable());
   }
 }