Implement interface types.

lib/compiler/implementation/ssa/nodes.dart

Index: lib/compiler/implementation/ssa/nodes.dart
diff --git a/lib/compiler/implementation/ssa/nodes.dart b/lib/compiler/implementation/ssa/nodes.dart
index 43e19ffc4ef6f394b57c69f82497bd927ed1a65c..b284027b422b6e5515835ec825b78b0e43d3943a 100644
--- a/lib/compiler/implementation/ssa/nodes.dart
+++ b/lib/compiler/implementation/ssa/nodes.dart
@@ -2079,11 +2079,10 @@ class HIndexAssign extends HInvokeStatic {
 }
 
 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];
@@ -2093,7 +2092,7 @@ class HIs extends HInstruction {
 
   accept(HVisitor visitor) => visitor.visitIs(this);
 
-  toString() => "$expression is $typeExpression";
+  toString() => "$expression is $typeName";
 }
 
 class HIfBlockInformation {