Hide bottom toolbar when empty in application panel's reports
Hide bottom toolbar when empty in application panel's reports

Screenshots:
before: https://i.imgur.com/E2bmpnf.png
after: https://i.imgur.com/Ahgtmx2.png

The toolbar is still shown when it contains items such as in the
`DatabaseTableView`.

Fixed: 1171755
Change-Id: I7ba56ec90397a470569d50a39e38ce4a292807d5
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2656242
Reviewed-by: Sigurd Schneider <f04d242e109628a27a0f75fd49a87722bcf291fd@chromium.org>
Commit-Queue: Wolfgang Beyer <573aa99bb19da47d816981118f95c945310dd3f4@chromium.org>

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