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* Remove DownloadShelfNeedsLayout().  The BrowserView implementation of
  this turned out to be equivalent to checking if the download shelf
  GetVisible() returns true.  BrowserViewLayout can do this directly.
  The test implementation of this was easy to replace with setting the
  visibility directly.

* Remove the SetViewVisibility() call in LayoutDownloadShelf().  The
  download shelf updates its own visibility (correctly), so this was a
  no-op.

* Remove the Layout() call in LayoutDownloadShelf().  If the View size
  has changed, SetBoundsRect() will Layout() automatically.  If not,
  layout is unnecessary.

* Better use of unique_ptr to convey ownership in unittest code.

Bug: none
Change-Id: Ia79970b1fd386a080623ff80c57eb29bc50c2d2a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2227435
Commit-Queue: Allen Bauer <kylixrd@chromium.org>
Reviewed-by: Allen Bauer <kylixrd@chromium.org>
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774638}