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This CL adds all remaining UI strings for UnifiedSystemTray. String
freeze will happen soon, so we have to make sure they land before that.

TEST=manual
BUG=813499

Change-Id: I8fed8fd079643fc37957a82628a24d09343fb70a
Reviewed-on: https://chromium-review.googlesource.com/1103435Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568305}