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MDCAppBar will soon be deprecated. This CL migrates all MDCAppBar code
to use MDCAppBarViewController.

It is basically following the migration guide here:
https://github.com/material-components/material-components-ios/tree/develop/components/AppBar#migration-guide-mdcappbar-to-mdcappbarviewcontroller

Bug: 874534
Change-Id: Ibe3ea272763b98bd7ded513111167221f06c9e6b
Reviewed-on: https://chromium-review.googlesource.com/1187402Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586042}