Add fuzzer for xxHash. Local testing did not turn up any crashes. Bug: angleproject:2983 Change-Id: I5e87ed0768e5bc4454c1a896f96d09ddd92baf44 Reviewed-on: https://chromium-review.googlesource.com/c/1458656 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>