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We would like some flexibility around the order of annoucement for
forthcoming features, so this CL removes the requirement that only
later messages are displayed, instead suppressing only the most
recently-displayed message. It also adds strings for file transfer
and multi-monitor and cleans up some of the CSS to handle long strings.

Change-Id: Iab73367c7a8f09d588b45c3d1a02514a83094a20
Reviewed-on: https://chromium-review.googlesource.com/c/1371074Reviewed-by: Joe Downing <joedow@chromium.org>
Commit-Queue: Jamie Walch <jamiewalch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615609}