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There are two paths to unminimize/restoring a window:
. Implicitly by calling Show()/Activate(). In this scenario the expectation
  is the Widget returns to it's pre-minimized state.
  DesktopWindowTreeHostMus does *not* cache the pre-minimized state, only
  the server knows it. While waiting for the server to change the show state
  it's important IsMinimized() returns false. To deal with this an observer is
  added to wait for the show state to change.
. By calling Restore(). Restore sets the state to normal, circumventing
  the pre-minimized state in the server. This mirrors what NativeWidgetAura
  does.

BUG=883523
TEST=covered by tests

Change-Id: I79a89a419032f125d905a98a01fe906c7ca82efd
Reviewed-on: https://chromium-review.googlesource.com/c/1299913
Commit-Queue: Scott Violet <sky@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603522}