tablet: Fix a bug with histograms logging with snapped windows.

They shouldn't be logged because there should be no animations when the
active window is snapped and we enter/exit tablet mode. This also
removes a workaround added to handle the maximized window case. This is
a follow up to [1].

[1] https://chromium-review.googlesource.com/c/chromium/src/+/1562717/8..14

Test: ash_unittests TabletModeControllerTest.TabletModeTransitionHistograms*
Bug: 948707
Change-Id: I74b89879d496f31a529e72946400c0aa2bd44319
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1595547
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#656928}
3 files changed