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Right now we only record a metric on when a voice search is triggered
in the omnibox, and nowhere else. This patch records where the start of
a voice interaction comes from, and if completed successfully resulting
in either suggestions or a navigation to a SRP, the source of the finish
event as well. This currently includes omnibox, NTP, and the search
widget.

This also includes a minor refactoring, pulling voice search logic out
LocationBarLayout and into its own class,
LocationBarVoiceRecognitionHandler.

Bug: 817228
Change-Id: Ie0a97ecbbec92c9189e4454e67c94b18ca4c7ffe
Reviewed-on: https://chromium-review.googlesource.com/943598
Commit-Queue: Troy Hildebrandt <thildebr@chromium.org>
Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Reviewed-by: Maria Khomenko <mariakhomenko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547560}