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Currently we only attempt to convert history provider suggestions to
tab switch suggestions. This change moves the code to autocomplete
result and calls it from the controller after settling on the best
matches.

Also moves the unit test.

Bug: 780835
Change-Id: Ide8e7998911455766b8157d6dcbf8d65d32fd179
Reviewed-on: https://chromium-review.googlesource.com/1007482
Commit-Queue: Kevin Bailey <krb@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551765}