Implement the new '?.' operator in analyzer.

tests/language/conditional_access_helper.dart

Index: tests/language/conditional_access_helper.dart
diff --git a/tests/language/conditional_access_helper.dart b/tests/language/conditional_access_helper.dart
new file mode 100644
index 0000000000000000000000000000000000000000..3b31e28313cb75d95b7ecf0438263a4508a00587
--- /dev/null
+++ b/tests/language/conditional_access_helper.dart
@@ -0,0 +1,16 @@
+// Copyright (c) 2015, 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.
+
+// Library used by conditional_property_assignment_test.dart,
+// conditional_property_access_test.dart, and
+// conditional_method_invocation_test.dart, all of which import it using the
+// prefix "h.".
+
+library lib;
+
+var topLevelVar;
+
+class C {
+  static var staticField;
+}