The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9f0c480da9cb188c82e16e6c6751875a60a114cf

commit 9f0c480da9cb188c82e16e6c6751875a60a114cf
Author: Rune Lillesveen <rune@opera.com>
Date: Wed Sep 27 02:59:59 2017

Reland "Store new ComputedStyle object if style did not change."

This is a reland of https://chromium-review.googlesource.com/681755

The comparison of ComputedStyle does not take additional flags into
account. For instance, the AffectedBy* flags used for updating pseudo
classes like :hover. We used to call SetStyleInternal, but this was
removed because the previous comment said it was because of style
sharing which is now removed.

The display:contents case (768406) never worked because the code path
for StoreNonLayoutObjectComputedStyle() was always skipped when
computed style compared to be equal.

TBR=nainar@chromium.org,treib@chromium.org

Bug:  768406 ,  767832 ,  768790 
Change-Id: Iee509e43e5fcc29d04944655d3d966ea61cc2adf
Reviewed-on: https://chromium-review.googlesource.com/684186
Commit-Queue: Rune Lillesveen <rune@opera.com>
Reviewed-by: Rune Lillesveen <rune@opera.com>
Cr-Commit-Position: refs/heads/master@{#504561}
[add] https://crrev.com/9f0c480da9cb188c82e16e6c6751875a60a114cf/third_party/WebKit/LayoutTests/fast/dynamic/hover-after-affected-by-change.html
[modify] https://crrev.com/9f0c480da9cb188c82e16e6c6751875a60a114cf/third_party/WebKit/Source/core/dom/Element.cpp