Sub-tasks:
1. Add "mac10.12" as a supported version in webkitpy/layout_tests/port/mac.py.
2. Set up "WebKit Mac10.12" on chromium.webkit
- Request slave, make CLs in src and build.
3. Set up "mac10.12_blink_rel" on chromium.webkit
- Request slave, make CLs in src and build.
4. Add new builders to webkitpy/common/config/builders.py.
Comment 1 by dpranke@chromium.org
, Mar 2 2017