Error previous listed is mx_port_queue failing with MX_ERR_INVALID_ARGS, most likely indicating that |port| isn't a valid port handle.

Read registration failure is:

[00000.801] 03179.03221> mx_object_wait_async_failed[3:2028579632:0708/020458.245169:801427:ERROR:message_pump_fuchsia.cc(107)] mx_object_wait_async failed: -12

This is an MX_ERR_WRONG_TYPE failure, again suggesting that we're passing an invalid |port| parameter.

While we're dependent on unstable/private mxio APIs we should ideally build on the ulib port API wrapper, which implements fd-watching, to benefit from updates/improvements to that in future SDK rolls.

Found threading bugs in some test fixtures, including the FileDescriptorWatcher POSIX wrapper, which would explain why this has been flakey - fixes are up for review at https://chromium-review.googlesource.com/c/565227.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/14e88d132b8de80803a825078fe16fd433410360

commit 14e88d132b8de80803a825078fe16fd433410360
Author: Wez <wez@chromium.org>
Date: Wed Jul 12 01:51:00 2017

Add extra CHECKs and DLOGs, and missing MX_PORT_OPT_V2.

This reverts https://chromium-review.googlesource.com/562660.

Our current Fuchsia SDK has a kernel version which supports both the
old ports API, and the new "V2" API, so we must pass the MX_PORT_OPT_V2
option, to create the right version of port. We will un-do this change,
and possibly migrate to using the ulib/port APIs, in future.

This CL also fixes StopWatchingFileDescriptor() to cope with being
called more than once, to match the API/interface expectations, adds
some additional Debug logging for API failures, and adds CHECKs on
calls which we cannot cope with seeing fail.

Bug:  740305 

Change-Id: I2579039fbd747e528da3c59cba9f2e1d07bf7326
Reviewed-on: https://chromium-review.googlesource.com/564739
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#485787}
[modify] https://crrev.com/14e88d132b8de80803a825078fe16fd433410360/base/message_loop/message_pump_fuchsia.cc