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1. Currently expand arrow exists in AppsContainerView, so opening search
   results page will move it off screen. To make it stay where it is and
   fade it out, we need to move it to ContentsView.
2. Make expand arrow focusable only in peeking state.

Demo: https://drive.google.com/open?id=1hgSqEDgEW1wZr5Dxw8WQmGpEosy4sDgP

Bug: 866690,868107
Change-Id: I965703041f498f8ad1e64c6db47718e7bf69c8f8
Reviewed-on: https://chromium-review.googlesource.com/1150900
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Reviewed-by: Yury Khmel <khmel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579494}