Fix focus after an interstitial is destroyed. (Merge to M60)

When an interstitial is created, it steals the page's focus. When it is
destroyed, it is supposed to return focus to the page, however, since
the WebContents still thinks an interstitial is being displayed, the
RenderWidgetHostImpl tries to maintain the focus on the interstitial.
This CL fixes that by moving the Focus() call into
WebContentsImpl::DetachInterstitialPage, instead of being called in
InterstitialPageImpl::Hide.

TBR=lfg@chromium.org

(cherry picked from commit 7f1241d2872150eb54fc10268ef03a2d2aca7bce)

Bug: 739676
Change-Id: I9eff1af3cb1500cc3f38400ae9e13e553bb0cf54
Reviewed-on: https://chromium-review.googlesource.com/565172
Reviewed-by: Charlie Reis <creis@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Commit-Queue: Lucas Gadani <lfg@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#485782}
Reviewed-on: https://chromium-review.googlesource.com/569843
Cr-Commit-Position: refs/branch-heads/3112@{#605}
Cr-Branched-From: b6460e24cf59f429d69de255538d0fc7a425ccf9-refs/heads/master@{#474897}
5 files changed