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This adds a CrosSmsService, a profile keyed service that
manages connection and pairing for ChromeOS Android Messages for
Web integration. This also includes a basic ConnectionManager
class that's listens for service worker events and
establishes connection. Message passing between service
worker and connection manager will be included in a follow up CL.
Design docs: go/awm-cros-service go/awm-cros

Bug: 850823
Change-Id: I792fbdad6aff6bc9391e4b0055e8e84a36bbd56e
Reviewed-on: https://chromium-review.googlesource.com/1140902
Commit-Queue: Azeem Arshad <azeemarshad@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Jeremy Klein <jlklein@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583512}