dart2js cps: 'is' checks on types with type arguments.

pkg/compiler/lib/src/cps_ir/type_propagation.dart

Index: pkg/compiler/lib/src/cps_ir/type_propagation.dart
diff --git a/pkg/compiler/lib/src/cps_ir/type_propagation.dart b/pkg/compiler/lib/src/cps_ir/type_propagation.dart
index 2a4307e2e7d01a333240b8505a433a61ccee1fdf..842d460e100272048de5271cc68f01f3cac6d5e4 100644
--- a/pkg/compiler/lib/src/cps_ir/type_propagation.dart
+++ b/pkg/compiler/lib/src/cps_ir/type_propagation.dart
@@ -301,7 +301,8 @@ class _TransformingVisitor<T> extends RecursiveVisitor {
   void visitTypeOperator(TypeOperator node) {
     Continuation cont = node.continuation.definition;
     LetPrim letPrim = constifyExpression(node, cont, () {
-      node.receiver.unlink();
+      node.value.unlink();
+      node.typeArguments.forEach((Reference ref) => ref.unlink());
       node.continuation.unlink();
     });
 
@@ -707,9 +708,10 @@ class _TypePropagationVisitor<T> implements Visitor {
     if (node.isTypeCast) {
       // TODO(jgruber): Add support for `as` casts.
       setValues(nonConstant());
+      return;
     }
 
-    _AbstractValue<T> cell = getValue(node.receiver.definition);
+    _AbstractValue<T> cell = getValue(node.value.definition);
     if (cell.isNothing) {
       return;  // And come back later.
     } else if (cell.isConstant && node.type.kind == types.TypeKind.INTERFACE) {