The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/dfe6cf582c76a362871d93821a25ee5af7037cc1

commit dfe6cf582c76a362871d93821a25ee5af7037cc1
Author: rune <rune@opera.com>
Date: Thu Aug 25 10:56:19 2016

Use LocalStyleChange for insertion point inheritance propagation.

For shadow dom v0, we used a SubtreeStyleChange for propagating
inherited style changes through insertion points to distributed nodes.
LocalStyleChange should suffice. We already use LocalStyleChange in the
HTMLSlotElement case.

We still need to use SubtreeStyleChange where we have a
SubtreeStyleChange/Force from further up the tree like:

<host>
  <:shadow-root>
    <style>.a::content * { background: green }</style>
    <div id="a">
      <content></content>
    </div>
  </:shadow-root>
  <div>Green when #a gets class a.</div>
</host>

R=kochi@chromium.org
BUG= 638869 

Review-Url: https://codereview.chromium.org/2258793003
Cr-Commit-Position: refs/heads/master@{#414386}

[add] https://crrev.com/dfe6cf582c76a362871d93821a25ee5af7037cc1/third_party/WebKit/LayoutTests/fast/css/invalidation/inherit-through-insertion-point-v0.html
[modify] https://crrev.com/dfe6cf582c76a362871d93821a25ee5af7037cc1/third_party/WebKit/Source/core/dom/shadow/InsertionPoint.cpp