dart2js cps: Keep interceptors in a separate field.

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

Index: pkg/compiler/lib/src/cps_ir/backward_null_check_remover.dart
diff --git a/pkg/compiler/lib/src/cps_ir/backward_null_check_remover.dart b/pkg/compiler/lib/src/cps_ir/backward_null_check_remover.dart
index de027ecdaef4059e88f6c7354f7e1cba0ffd2669..41bb65eb758871da69e4fdd0dee4a0e023ab16d9 100644
--- a/pkg/compiler/lib/src/cps_ir/backward_null_check_remover.dart
+++ b/pkg/compiler/lib/src/cps_ir/backward_null_check_remover.dart
@@ -59,7 +59,7 @@ class BackwardNullCheckRemover extends BlockVisitor implements Pass {
     if (prim is SetField) return prim.object;
     if (prim is SetIndex) return prim.object;
     if (prim is InvokeMethod && !selectorsOnNull.contains(prim.selector)) {
-      return prim.dartReceiver;
+      return prim.receiver;
     }
     if (prim is ForeignCode) {
       return prim.isNullGuardOnNullFirstArgument() ? prim.argument(0) : null;