Implement interface types.

lib/compiler/implementation/ssa/nodes.dart

 // 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.
 
 interface HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBitAnd(HBitAnd node);
   R visitBitNot(HBitNot node);
   R visitBitOr(HBitOr node);
   R visitBitXor(HBitXor node);
@@ skipping 2061 matching lines @@
   }
 
   bool get builtin() => receiver.isMutableArray();
   HType computeType() => value.type;
   // This instruction does not yield a new value, so it always
   // has the expected type (void).
   bool hasExpectedType() => true;
 }
 
 class HIs extends HInstruction {
-  // TODO(ahe): This should be a Type, not Element.
-  final Element typeExpression;
+  final Type typeName;
   final bool nullOk;
 
-  HIs(this.typeExpression, HInstruction expression, [nullOk = false])
+  HIs(this.typeName, HInstruction expression, [nullOk = false])
     : this.nullOk = nullOk, super(<HInstruction>[expression]);
 
   HInstruction get expression() => inputs[0];
 
   HType computeType() => HType.BOOLEAN;
   bool hasExpectedType() => true;
 
   accept(HVisitor visitor) => visitor.visitIs(this);
 
-  toString() => "$expression is $typeExpression";
+  toString() => "$expression is $typeName";
 }
 
 class HIfBlockInformation {
   final HIf branch;
   final SubGraph thenGraph;
   final SubGraph elseGraph;
   final HBasicBlock joinBlock;
   HIfBlockInformation(this.branch,
                       this.thenGraph,
                       this.elseGraph,
                       this.joinBlock);
 }