dart2js cps_ir: Use interceptors for is-checks (version 2)

pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart

Index: pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
diff --git a/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart b/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
index 8adf3a9171e3a46432e915c49a531b6d1b8fd60c..e5cd0e658130e8b395f26b7fd9cbe0946b123411 100644
--- a/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
+++ b/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
@@ -641,6 +641,12 @@ class Builder implements cps_ir.Visitor/*<NodeCallback|Node>*/ {
     return new TypeOperator(value, node.dartType, typeArgs, isTypeTest: true);
   }
 
+  Expression visitTypeTestViaFlag(cps_ir.TypeTestViaFlag node) {
+    Expression value = getVariableUse(node.interceptor);
+    // TODO(sra): Move !! to cps_ir level.
+    return new Not(new Not(new GetTypeTestProperty(value, node.dartType)));
+  }
+
   Expression visitGetStatic(cps_ir.GetStatic node) {
     return new GetStatic(node.element, node.sourceInformation);
   }
@@ -700,4 +706,3 @@ class Builder implements cps_ir.Visitor/*<NodeCallback|Node>*/ {
   visitContinuation(cps_ir.Continuation node) => unexpectedNode(node);
   visitMutableVariable(cps_ir.MutableVariable node) => unexpectedNode(node);
 }
-