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This is no longer used and has been getting increasingly buggy as Chrome
and macOS evolve (see bugs 762915, 983451, 1020622, 1078158, 1098786).
The two uses have since been removed, so remove the support code.

Bug: 1111423
Change-Id: I07b5268dd07c2659ed1bd710bfaae704804e5daf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2347000
Commit-Queue: David Benjamin <davidben@chromium.org>
Auto-Submit: David Benjamin <davidben@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799746}