Add Crostini VMs to task manager listing

This adds the Crostini VMs to the process listings in task manager. It
does this by walking the process tree and getting the vm_concierge PID,
which is the parent of all VM processes. It then finds the children of
that which are 'crosvm' processes and those are the VMs. It also
extracts the name of the VM from the command line for the process since
it exists there as a base64 encoded value.

Bug: chromium:703953
Test: Manually verified on eve with multiple VMs
Change-Id: Iab47aaa78b1edc4c7d581c282b1bbeacf9977e84
Reviewed-on: https://chromium-review.googlesource.com/c/1265029
Commit-Queue: Jeffrey Kardatzke <jkardatzke@google.com>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Toni Baržić <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598522}
10 files changed