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These settings no longer hook up to actual data; they just return
'allow' always, and setting them has no effect. Updated documentation.

This is because Chrome now (and has for awhile) ignores these settings
and always permits these actions without asking the user.

BUG=591896

Review-Url: https://codereview.chromium.org/2358893004
Cr-Commit-Position: refs/heads/master@{#422716}