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This cl adds the templating engine which is used to generate the proto
and the harness used by the fuzzer. The templater uses Jinja2 and has a
.gni wrapper for ease of use in our build system.

I have confirmed that the fuzzer has more coverage than the prototype
in crrev.com/c/1640526, however it requires further work to improve
the coverage to the desired levels.

Bug: 961564
Change-Id: Ie27d7ff0b97cf3ed88dadfebf4d977682054c699
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1645134Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Timothy Loh <timloh@chromium.org>
Reviewed-by: Oliver Chang <ochang@chromium.org>
Commit-Queue: Nic Hollingum <hollingum@google.com>
Cr-Commit-Position: refs/heads/master@{#669918}