Convert 'CFI Linux ToT' buildbot to GN.
Convert 'CFI Linux ToT' buildbot to GN.

Also, make it build an official Chrome. We want to track regressions
for the link time constantly, as the cost of a late surprise is very high:
wait for a new Clang toolchain roll.

BUG=568384

Review URL: https://codereview.chromium.org/1529973003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#365436}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk