Fix handle_watcher when start is called twice on the same handle.
This carries over a fix by qsr@ for the mojo helper handle_watcher
landed in the mojo repo in https://codereview.chromium.org/781753004.
The fix allows the network service apptests not to crash when built
against the Chromium copy of mojo/common.
BUG=450356
Review URL: https://codereview.chromium.org/878513003
Cr-Commit-Position: refs/heads/master@{#313261}
CrOS-Libchrome-Original-Commit: 5e9a3adac10fdf8d172de5aa0d7ec9a7bbb1e441
2 files changed