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This paves the way to plug in an AutocompleteController, and associated
UI.  Also, drive URL bar and WebVR toast state via model, as omnibox
will require some of the same data.

BUG=777542
R=vollick

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I29e96b5318e0d90b5530c12166db9fe780dba276
Reviewed-on: https://chromium-review.googlesource.com/772393
Commit-Queue: Christopher Grant <cjgrant@chromium.org>
Reviewed-by: Biao She <bshe@chromium.org>
Reviewed-by: Ian Vollick <vollick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517519}