Re-apply change https://codereview.webrtc.org/1426673007/

Do not delete the turn port entry right away when the respective
connection is deleted. The dependency on asyncinvoker has been added
in chromium libjingle-nacl.

BUG=webrtc:5120

Review URL: https://codereview.webrtc.org/1450263002

Cr-Original-Commit-Position: refs/heads/master@{#10679}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 32f39968ce79cfca5146069e410ded2f104bba23
3 files changed