We patch NavigationRequest::OnStartChecksComplete to call
MaybeHideReferrer. One of the params to MaybeHideReferrer is top
document GURL which was available in OnStartCheckComplete. The Chromium
change below removed it. Added a chromium_src override that includes
GetTopDocumentGURL function that containes the deleted functionality.

Chromium change:

https://chromium.googlesource.com/chromium/src/+/435bcb58bb2c75be8276f1dde69fc6c9891c45ba

commit 435bcb58bb2c75be8276f1dde69fc6c9891c45ba
Author: Lukasz Anforowicz <lukasza@chromium.org>
Date:   Fri Jul 12 20:50:06 2019 +0000

    Store |initiator_origin| in FrameNavigationEntry.

    Changes in this CL
    ==================

    This CL:

    1. Updates FrameNavigationEntry::UpdateEntry and
       FrameNavigationEntry's constructor so that they both take
       |const base::Optional<url::Origin>& initiator_origin| which
       gets stored in a new FrameNavigationEntry::initiator_origin_ field.

    2. Updates callers of FNE::UpdateEntry and FNE's constructor to
       provide/propagate the initiator as needed.  This includes
       adding an |initiator_origin| parameter to
       - NavigationEntryImpl's constructor
       - NavigationEntryImpl::AddOrUpdateFrameEntry
       - NavigationController::CreateNavigationEntry
       (the list above is not necessarily exhaustive/complete)

    3. Uses the new |FrameNavigationEntry::initiator_origin()| from
       NavigationEntryImpl::ConstructCommonNavigationParams (which
       used to always provide |base::nullopt| initiator for history
       navigations - always treating them as browser-initiated, rather
       than replaying the original initiator).

    The changes above makes sure that the right Sec-Fetch-Site http request header is
    "replayed" during history navigations.  The CL adds browser tests and
    WPT tests to cover the new, desired behavior.

    Follow-up changes
    =================

    This CL does not:

    - Use |FrameNavigationEntry::initiator_origin()| in GetOriginForURLLoaderFactory
      in render_frame_host_impl.cc (this will be done in a follow-up CL at
      https://crrev.com/c/1672176)

    - Handle persisting |FrameNavigationEntry::initiator_origin()| for
      session restore (this is tracked in a separate https://crbug.com/976055).

    Bug: 946503