Add a "WebKit Linux ASAN" builder mapping.

This allows garden-o-matic to handle ASAN rebaselines.

BUG=333903
R=dpranke@chromium.org

Review URL: https://codereview.chromium.org/137063002

git-svn-id: svn://svn.chromium.org/blink/trunk@165032 bbb929c8-8fbe-4397-9dbb-9b2b20218538