Move continueWithExpression to IrBuilder.

sdk/lib/_internal/compiler/implementation/cps_ir/cps_ir_nodes.dart

Index: sdk/lib/_internal/compiler/implementation/cps_ir/cps_ir_nodes.dart
diff --git a/sdk/lib/_internal/compiler/implementation/cps_ir/cps_ir_nodes.dart b/sdk/lib/_internal/compiler/implementation/cps_ir/cps_ir_nodes.dart
index 5721678910abae3ba22017e5560b9c69fa8ae8d4..4ea9bebb5900e8c8b9236a5ab003c9ac7846253d 100644
--- a/sdk/lib/_internal/compiler/implementation/cps_ir/cps_ir_nodes.dart
+++ b/sdk/lib/_internal/compiler/implementation/cps_ir/cps_ir_nodes.dart
@@ -283,17 +283,20 @@ class TypeOperator extends Expression {
   final Reference receiver;
   final DartType type;
   final Reference continuation;
-  final String operator;
+  // TODO(johnniwinther): Use `Operator` class to encapsule the operator type.
+  final bool isTypeTest;
 
-  TypeOperator(this.operator,
-                Primitive receiver,
-                this.type,
-                Continuation cont)
+  TypeOperator(Primitive receiver,
+               this.type,
+               Continuation cont,
+               {bool this.isTypeTest})
       : this.receiver = new Reference(receiver),
         this.continuation = new Reference(cont) {
-    assert(operator == "is" || operator == "as");
+    assert(isTypeTest != null);
   }
 
+  bool get isTypeCast => !isTypeTest;
+
   accept(Visitor visitor) => visitor.visitTypeOperator(this);
 }