The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/916b109ded853d592d1585297ba16a46ce1ac882

commit 916b109ded853d592d1585297ba16a46ce1ac882
Author: Hitoshi Yoshida <peria@chromium.org>
Date: Wed Sep 12 02:14:10 2018

Revert "Add another BeforeUnloadType in support of discarding."

This reverts commit e200b3b1e457e2a674992fbeeb2bf5541095e515.

Reason for revert: This CL seems to break tests. See  issue 883160  for details

Original change's description:
> Add another BeforeUnloadType in support of discarding.
> 
> In order to not discard sites with potential unsaved user state it is necessary
> to run beforeunload handlers to see if they return the empty string or not. When running
> handlers in this context it is undesirable to launch a modal dialog, but rather to
> silently block the discard and continue running the page.
> 
> This CL adds a new BeforeUnloadType to RenderFrameHostImpl in support of this. A
> follow-up change will expose functionality for invoking DispatchBeforeUnload with
> this BeforeUnloadType, and returning the results of the unload via a callback.
> 
> BUG=877550
> 
> Change-Id: Iad029fb0f70f9f44695f15c5ca0c0f6e4ed7ff78
> Reviewed-on: https://chromium-review.googlesource.com/1208962
> Commit-Queue: Chris Hamilton <chrisha@chromium.org>
> Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#590362}

TBR=chrisha@chromium.org,alexmos@chromium.org

Change-Id: If974ab384c3fdda13ca8e3eb89940d5a4026fa68
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 877550,  883160 
Reviewed-on: https://chromium-review.googlesource.com/1220408
Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Commit-Queue: Hitoshi Yoshida <peria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590575}
[modify] https://crrev.com/916b109ded853d592d1585297ba16a46ce1ac882/content/browser/frame_host/render_frame_host_impl.cc
[modify] https://crrev.com/916b109ded853d592d1585297ba16a46ce1ac882/content/browser/frame_host/render_frame_host_impl.h
[modify] https://crrev.com/916b109ded853d592d1585297ba16a46ce1ac882/content/browser/frame_host/render_frame_host_impl_browsertest.cc
[modify] https://crrev.com/916b109ded853d592d1585297ba16a46ce1ac882/content/browser/web_contents/web_contents_impl.h

This was actually due to an use-of-uninitialized-value in existing code, but tasak@ fixed that here:

https://chromium.googlesource.com/chromium/src/+/eac696a12a263f85796eca7fd1cb4bf31565208c

I'll be relanding my CL as is.