[code coverage] Add fuzzer target.

This change adds a single fuzzer target to the continuous code coverage
bot and the matching trybot.

R=stgao,liaoyuke,jbudorick,mmoroz

Change-Id: Iab4af3dbfcfbce608b42a3089913f30d6753382d
Reviewed-on: https://chromium-review.googlesource.com/c/1364690
Commit-Queue: Roberto Carrillo <robertocn@chromium.org>
Reviewed-by: Shuotao Gao <stgao@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Reviewed-by: Max Moroz <mmoroz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615486}
7 files changed