dart2js cps: More aggressive operator specialization.

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

Index: pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
index 37836bf77175f1470426782a107b5df8df90a894..952f881fcc9d9f612fe9baaec757745e6495686d 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
@@ -448,10 +448,11 @@ class SExpressionStringifier extends Indentation implements Visitor<String> {
     return '(BoundsCheck $object $index $length ${node.checkString})';
   }
 
-  String visitNullCheck(NullCheck node) {
+  String visitReceiverCheck(ReceiverCheck node) {
     String value = access(node.value);
     String condition = optionalAccess(node.condition);
-    return '(NullCheck $value $condition (${node.selector ?? ""}))';
+    return '(ReceiverCheck $value ${node.selector} $condition '
+        '${node.flagString}))';
   }
 }