Revert "Add pre- and post-commit modes to LoginHandler"

This reverts commit a6f001aebce818cc656b99b0d5e7ad76d2a95415.

Reason for revert: Speculative. These 3 tests started failing
on all main waterfall mac tester bots in browser_tests:
ServiceProcessControlBrowserTest.HistogramsNoService
ServiceProcessControlBrowserTest.LaunchAndIPC
ServiceProcessControlBrowserTest.LaunchAndReconnect

All builds where this started happening had this CL in common.
The build that best shows this is:
https://ci.chromium.org/p/chromium/builders/ci/Mac10.11%20Tests/37949
The other 3 CLs in that build look like they're likely no-ops on macOS.

This CL also doesn't look super related to the failure message, but
relanding is easy if this turns out to not help.
Original change's description:
> Add pre- and post-commit modes to LoginHandler
> 
> LoginHandler currently handles two tasks when showing an interstitial:
> running the request through extensions and then showing a login
> prompt. When converted to committed interstitials, we need to run the
> request through extensions before the navigation commits, and then
> show a login prompt on top of a committed error page. This CL adds a
> "mode" argument to LoginHandler. When committed interstitials are
> enabled, the "mode" argument determines whether we should just run the
> request through extensions and then cancel it (pre-commit mode), or
> show a login prompt (post-commit). The post-commit mode is currently
> not reachable; we'll use it once we add the WebContentsObserver that
> observes the committed error page (https://crbug.com/963313).
> 
> Note: this "mode" design is kind of messy and we'll probably want to
> come back and clean it up later. For now, it's the simplest way to
> leave LoginHandler intact for when committed interstitials are
> disabled, and use the parts of it that we need before+after commit
> when committed interstitials are enabled. Once committed interstitials
> land and we clean up the old code, we will probably want to split
> LoginHandler into two classes rather than having one class that can
> operate in two different modes.
> 
> Bug: 963311
> Change-Id: I1efddb3eca3a6b822135bd721db05f2f47561a86
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1616943
> Reviewed-by: Carlos IL <carlosil@chromium.org>
> Reviewed-by: Joe DeBlasio <jdeblasio@chromium.org>
> Commit-Queue: Emily Stark <estark@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#661141}

TBR=estark@chromium.org,carlosil@chromium.org,jdeblasio@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 963311
Change-Id: Id22a831ac81cd1056da31efbf5f045edb5533726
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1619069
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661206}
4 files changed