When all connections timed out on writing, delete them all.
BUG=5111

Review URL: https://codereview.webrtc.org/1421123003

Cr-Original-Commit-Position: refs/heads/master@{#10431}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 77d0d6e858203cbc559b2f5d6ffabb7bc2fcb8e6
3 files changed