The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fab3cb6373039518bde0d5467c63c2d9d125d2b2

commit fab3cb6373039518bde0d5467c63c2d9d125d2b2
Author: Pavel Feldman <pfeldman@chromium.org>
Date: Thu Oct 05 01:02:01 2017

DevTools: handle the case when protocol is handling the JS dialog without dialog delegate.

Bug:  771000 
Change-Id: I396cd5427784f9624b9bc93c9dccc7150252f0f0
Reviewed-on: https://chromium-review.googlesource.com/701403
Commit-Queue: Pavel Feldman <pfeldman@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506597}
[modify] https://crrev.com/fab3cb6373039518bde0d5467c63c2d9d125d2b2/content/browser/devtools/protocol/devtools_protocol_browsertest.cc
[modify] https://crrev.com/fab3cb6373039518bde0d5467c63c2d9d125d2b2/content/browser/devtools/protocol/page_handler.cc
[modify] https://crrev.com/fab3cb6373039518bde0d5467c63c2d9d125d2b2/content/browser/web_contents/web_contents_impl.cc
[modify] https://crrev.com/fab3cb6373039518bde0d5467c63c2d9d125d2b2/content/browser/web_contents/web_contents_impl.h