Make dump messages asynchronous.

Prevents the dump actions from being blocked by traversals.

Removed a stale comment on queueOrSendMessage and renamed it to
reflect its current implementation since it no longer has a secondary
queue.  Removed an unnecessary lock as well.

Bug: 10948648
Change-Id: Ic5fcc567212fb9cc07566c12f5f419af13c2b0b1