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Add a simple perf test for SubstringSetMatcher. I plan to change a bit
of the internal implementation, so this will help to measure any perf
difference as well as catch future regressions.

BUG=974391

Change-Id: I03ad4d2ae531c524256db095285761ea4529b270
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2038070Reviewed-by: Dominic Battré <battre@chromium.org>
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738709}