This was causing mojo_public_bindings_unittests' MultiplexRouterTest.BasicRequestResponse and MultiplexRouterTest.RequestWithNoReceiver to fail with the new EDK. The problem is that in Connector::HandleError message_pipe_ is reset to a dummy message pipe whose other end is closed immediately. In the old EDK, the live end notices that the peer is closed synchronously. In the new EDK this happens asynchronously because of thread hops to the IO thread. The fix is to simply ensure we don't watch the message pipe handle twice (since it's not cancelled immediately).
BUG=561803
Review URL: https://codereview.chromium.org/1557753002
Cr-Commit-Position: refs/heads/master@{#367327}
Mojo is an effort to extract a common platform out of Chrome's renderer and
plugin processes that can support multiple types of sandboxed content, such as
HTML, Pepper, or NaCl.