Remove XP port from Blink LayoutTest related scripts.
Fixing up unit tests was somewhat complex due to XP being
used as a key test case throughout. We have essentially
updated the unit tests here to treat Win7 as the new XP,
and Win10 the way Win7 was previously.
Also remove dead ALL_BASELINE_VARIANTS constant and
accessor methods, and document the one remaining
(used by queries_unittest.py) for subsequent cleanup.
BUG=581240
Review URL: https://codereview.chromium.org/1624373005
Cr-Commit-Position: refs/heads/master@{#371701}
17 files changed
