Correctly skip if-null expressions.

tests/language/regress_26543_1_test.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
+// BSD-style license that can be found in the LICENSE file. 
+
+// Regression test for issue 26543
 
 class C {
-  static var _privateField = 42;
+  var x;
+  C() : x = null ?? <int, int>{} {}
 }
 
-get privateFieldSymbolInOther => #_privateField;
+main() {
+  print(new C());
+}