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Now one perf test combines several change types. We don't actually care
about relative small performance changes for each change type, but care
more about larger overall changes.

BTW add an OWNERS file containing pdr, schenney and wangxianzhu
for perf_tests/paint.

Change-Id: I3e88b7c2e6f304dfa80a28b2847704850079b536
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2380497Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#802822}