Add a new LPM fuzzer for Mach message servers.

This fuzzer tool allows modeling the complex Mach IPC structures,
including the generation and transfer of port rights. It also adds a
build rule to convert textproto to binarypb, so that the seed corpus for
these fuzzers can be human-editable/readable.

Adds a simple fuzzer for the MachPortRendezvousServer.

Bug: 932175
Change-Id: I909e4a8bac802ea1d4d73d26fcb0834803324360
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1526561
Reviewed-by: Mark Mentovai <mark@chromium.org>
Reviewed-by: Jonathan Metzman <metzman@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641854}
11 files changed