Window manager cleanup.

Specifically:
 - Fix policy vs wm lock management issues.
 - Share runnable to avoid allocation.
 - Remove unused noop runnable.
 - Make sure to handle status bar = null case.
 - Fix javadoc typo.

Bug: 8890313
Change-Id: I242eaef8e946025f6885d6dba3225722fb0ca7ce