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This is identical to the original CL (https://crrev.com/c/2462560).
The fix happened on the predecessor CL (https://crrev.com/c/2466739).

Original change's description:

> This replaces the use of ash::TabletMode and ash::TabletModeObserver in
> BrowserNonClientFrameViewAsh.
>
> This corresponds to phase 2.6 on the design document [1].
>
> Covered by existing tests, eg
>
> BrowserNonClientFrameViewAshTest.BrowserHeaderVisibilityInTabletModeTest
> HomeLauncherBrowserNonClientFrameViewAshTest.TabletModeBrowserCaptionButtonVisibility
>
> [1] https://docs.google.com/document/d/1xHwcHrAiEaWuA4usGEqKZ9zm1H8SGk3WkS-Jf2Q_los/
>
> BUG=1113900
> R=jamescook@chromium.org, sky@chromium.org
>
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2462560
> Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
> Reviewed-by: James Cook <jamescook@chromium.org>
> Reviewed-by: Scott Violet <sky@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#816316}

TBR=jamescook@chromium.org

Change-Id: Ic9cc488266a42ca4efc40fdfe4edbf7e00c8f93c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2468496
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Reviewed-by: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#816712}