Add support for precursor origin to Blink's SecurityOrigin.

This CL is part of adding precursor origin support to Chromium which
nick@ started in https://crrev.com/c/1028985. It adds the precursor
origin to Blink's SecurityOrigin class.

Bug: 882053
Change-Id: Ief9c1cf3c1008a0ce0ee52cf064e35aa8793f639
Reviewed-on: https://chromium-review.googlesource.com/c/1229180
Commit-Queue: Nasko Oskov <nasko@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598361}
6 files changed