[BrowserSwitcher] Mark ExternalGreylist policy for M77

The policy is not completely implemented yet, so it should have been
marked 'future'.

Bug: 958659
Change-Id: I814d39f998de5d55466e95fbeaf2d70a11dcfc5a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1630975
Commit-Queue: Pavol Marko <pmarko@chromium.org>
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Auto-Submit: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663962}
2 files changed