The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1c0152d0297a8341498a04087587b26ee59fbdda

commit 1c0152d0297a8341498a04087587b26ee59fbdda
Author: Yoshifumi Inoue <yosin@chromium.org>
Date: Mon Mar 19 06:51:38 2018

Make Selection#{base,extent}{Node,Offset} as aliases of {anchor,focus}{Node,Offset}

This patch makes |Selection#{base,extent}{Node,Offset}| as aliases of
|Selection#{anchor,focus}{Node,Offset}| instead of getting position from
|VisibleSelection| which we don't want to expose to JavaScript.

Note: Selection#{base,extent}{Node,Offset} are not standard API and there
are some discussion for standardizing them[1].

[1] https://github.com/w3c/selection-api/issues/34
Specify baseNode/baseOffset/extentNode/extentOffset?

Bug: 701501
Change-Id: I34fcdb4e80d5cef49bc1e0bdaea3cdec5c8b3758
Reviewed-on: https://chromium-review.googlesource.com/965663
Reviewed-by: Yoichi Osato <yoichio@chromium.org>
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543982}
[modify] https://crrev.com/1c0152d0297a8341498a04087587b26ee59fbdda/third_party/WebKit/Source/core/editing/DOMSelection.cpp