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The collapse state of the status area should be updated when the shelf state or
bounds change or when a tray item is shown or hidden.

Note that the actual calculation for which trays should be hidden or visible is
unimplemented and will be finished in a future CL.

TEST=unit test
BUG=982511

Change-Id: Ie4a46be7d03435bf8927062af0c7726f5cc090a3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1904165
Commit-Queue: Tim Song <tengs@chromium.org>
Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714798}