[9] Code Review Request For 8156170: Clean up Stage and StageHelper

[Chien Yang]

Hi Kevin and Jonathan,

Please review the proposed fix:

JIRA: https://bugs.openjdk.java.net/browse/JDK-8156170
Webrev: http://cr.openjdk.java.net/~ckyang/JDK-8156170/webrev.00/

- Chien