Revert "wm: Update nested activation handling"

This reverts commit ecde845099001740fee119a82d45664e622d0ade.

Reason for revert:
EXPECT_DEATH_IF_SUPPORTED not working in NDEBUG without DCHECK.

Original change's description:
> wm: Update nested activation handling
> 
> - NOTREACHED() and no-ope if the nested activation wants to change
>   to a different active window other than the one being activated;
> - Allow focus shift in nested activations as long as they don't
>   change the window to be activated
> 
> Bug: 908524
> Test: FocusControllerApiTest.ActivateWhileActivating
> Change-Id: I105c85bf2671c7e396fdcbedff7b8082f007f642
> Reviewed-on: https://chromium-review.googlesource.com/c/1357017
> Reviewed-by: Scott Violet <sky@chromium.org>
> Reviewed-by: Mitsuru Oshima (gardener - slow) <oshima@chromium.org>
> Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#616346}

TBR=xiyuan@chromium.org,sky@chromium.org,oshima@chromium.org

Change-Id: I8fd73d291c7a6774b1f48049d618a232340e936e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 908524
Reviewed-on: https://chromium-review.googlesource.com/c/1376137
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616375}
3 files changed