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Add a new BottomToolbarTest class with two simple tests that check
bottom toolbar visibilty and tab switcher button click handling.

Also updates chrome/android/java/.../toolbar/OWNERS file to include
twellington@ and chrome/android/javatests/.../toolbar/OWNERS file to
point to non-test OWNERS file.

BUG=1008212

Change-Id: I46839e3b614a68af5c75bf876f3c47565db63e84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1825787Reviewed-by: Matthew Jones <mdjones@chromium.org>
Commit-Queue: Theresa  <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#700260}