IsEquivalent(const Position& a, const Position& b) can be implemented as
a.ToOffsetInAnchor() == b.toOffsetInAnchor()
but this is slow if offset is large.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4aee85c54527cbd0857b07d6dc4699465f55a18f

commit 4aee85c54527cbd0857b07d6dc4699465f55a18f
Author: yosin <yosin@chromium.org>
Date: Mon May 15 07:35:00 2017

Introduce Position::IsEquivalent()

This patch introduces |Position::IsEquivalent()| to check whether two positions
are in same position regardless anchor type, e.g. |Position(node, 0)| and
|Position::FirstPositionInNode(node)|. denote a position before first child of
|node|.

This patch is a preparation of patch[1].

[1] http://crrev.com/2875933004: Utilize Position::IsEquivalent() in
{Up,Down}streamIgnoringEditingBoundaries()

BUG=716093, 719343
TEST=run_webkit_unit_tests --gtest_filter=PositionTest.IsEquivalent

Review-Url: https://codereview.chromium.org/2875253002
Cr-Commit-Position: refs/heads/master@{#471689}

[modify] https://crrev.com/4aee85c54527cbd0857b07d6dc4699465f55a18f/third_party/WebKit/Source/core/editing/Position.cpp
[modify] https://crrev.com/4aee85c54527cbd0857b07d6dc4699465f55a18f/third_party/WebKit/Source/core/editing/Position.h
[modify] https://crrev.com/4aee85c54527cbd0857b07d6dc4699465f55a18f/third_party/WebKit/Source/core/editing/PositionTest.cpp

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b67267c9b096b7ac8fd187bccd91178c04689e32

commit b67267c9b096b7ac8fd187bccd91178c04689e32
Author: Yoshifumi Inoue <yosin@chromium.org>
Date: Fri May 19 10:29:37 2017

Introduce Position::IsEquivalent()

This patch introduces |Position::IsEquivalent()| to check whether two positions
are in same position regardless anchor type, e.g. |Position(node, 0)| and
|Position::FirstPositionInNode(node)|. denote a position before first child of
|node|.

This patch is a preparation of patch[1].

[1] http://crrev.com/2875933004: Utilize Position::IsEquivalent() in
{Up,Down}streamIgnoringEditingBoundaries()

BUG=716093, 719343
TEST=run_webkit_unit_tests --gtest_filter=PositionTest.IsEquivalent

Review-Url: https://codereview.chromium.org/2875253002
Cr-Original-Commit-Position: refs/heads/master@{#471689}
Review-Url: https://codereview.chromium.org/2890403002 .
Cr-Commit-Position: refs/branch-heads/3071@{#628}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}

[modify] https://crrev.com/b67267c9b096b7ac8fd187bccd91178c04689e32/third_party/WebKit/Source/core/editing/Position.cpp
[modify] https://crrev.com/b67267c9b096b7ac8fd187bccd91178c04689e32/third_party/WebKit/Source/core/editing/Position.h
[modify] https://crrev.com/b67267c9b096b7ac8fd187bccd91178c04689e32/third_party/WebKit/Source/core/editing/PositionTest.cpp

This issue has been Available for over a year. If it's no longer important or seems unlikely to be fixed, please consider closing it out. If it is important, please re-triage the issue.

Sorry for the inconvenience if the bug really should have been left as Available.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot