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This patch adds a feedback source for the split toolbar that
identifies whether the feature is enabled.

Change-Id: I5a1455c246e9ad5a6a2d36a452a580678fe59dd0
Reviewed-on: https://chromium-review.googlesource.com/1181575Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584781}