Reland "[ios] Dismiss keyboard when navigating to chrome://flags in test."

This reverts commit 5f5495bb86fccbe94d414dc1b2f8421133847c7b.

Reason for revert: Don't wait for keyboard animation.

Original change's description:
> Revert "[ios] Dismiss keyboard when navigating to chrome://flags in test."
>
> This reverts commit 99473df8b2ec0d7ab43b776225c8eb97a724903e.
>
> Reason for revert: Not always working.
>
> Original change's description:
> > [ios] Dismiss keyboard when navigating to chrome://flags in test.
> >
> > On iOS 13 chrome://flags presents the keyboard which does not allow
> > tapping on back button.
> >
> > Bug: 977707
> > Change-Id: Ia0da9e063b894da4fbfccfb12d7d839774c3b230
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1666731
> > Commit-Queue: Eugene But <eugenebut@chromium.org>
> > Auto-Submit: Justin Cohen <justincohen@chromium.org>
> > Reviewed-by: Mike Dougherty <michaeldo@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#673082}
>
> TBR=justincohen@chromium.org,eugenebut@chromium.org,michaeldo@chromium.org
>
> Change-Id: Ia4a2f62f4bbd3a9ab46f314b209d09d0f0cb5b61
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 977707
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1681438
> Reviewed-by: Justin Cohen <justincohen@chromium.org>
> Commit-Queue: Justin Cohen <justincohen@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#673179}

TBR=justincohen@chromium.org,eugenebut@chromium.org,michaeldo@chromium.org

Change-Id: I6fe54aa0a434fa9d837a04df7ed6853e4f62a1c0
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 977707
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1681442
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Mike Dougherty <michaeldo@chromium.org>
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#673314}