dart2js cps_ir: Use interceptors for is-checks.

pkg/compiler/lib/src/js_backend/codegen/unsugar.dart

Index: pkg/compiler/lib/src/js_backend/codegen/unsugar.dart
diff --git a/pkg/compiler/lib/src/js_backend/codegen/unsugar.dart b/pkg/compiler/lib/src/js_backend/codegen/unsugar.dart
index 3f68eed7bee66f6c2bdc18a92988536dd6563611..60897e26e168649b14b0ef24f1b650b6c2726bf8 100644
--- a/pkg/compiler/lib/src/js_backend/codegen/unsugar.dart
+++ b/pkg/compiler/lib/src/js_backend/codegen/unsugar.dart
@@ -229,6 +229,18 @@ class UnsugarVisitor extends RecursiveVisitor implements Pass {
     // worry about unlinking.
   }
 
+  // TODO(sra): Insert interceptor on demand when we discover we want to use one
+  // rather than on every check.
+  processTypeTestRaw(TypeTestRaw node) {
+    assert(node.interceptor == null);
+    Primitive receiver = node.value.definition;
+    Primitive interceptor = new Interceptor(receiver, node.sourceInformation)
+        ..interceptedClasses.addAll(_glue.interceptedClasses);
+    insertLetPrim(interceptor, node.parent);
+    node.interceptor = new Reference<Primitive>(interceptor);
+    node.interceptor.parent = node;
+  }
+
   processInvokeMethod(InvokeMethod node) {
     Selector selector = node.selector;
     if (!_glue.isInterceptedSelector(selector)) return;