Firefox is buggy in that example. It shows both paragraphs with black text (yes it does support ::first-line, I checked).

Chrome and Firefox differ in how they break, marking as interop bug.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3f2d0c6bbce99fc2880356ff2ebfd323b5bcd8bc

commit 3f2d0c6bbce99fc2880356ff2ebfd323b5bcd8bc
Author: rune <rune@opera.com>
Date: Tue Mar 07 16:09:10 2017

Make ::first-line invalidation work when added or removed.

We were only invalidating ::first-line properly when both old and new
ComputedStyle contained ::first-line styles. Now, instead call
setNeedsLayoutAndPrefWidthsRecalc to trigger changes when either old or
new ComputedStyle does not have ::first-line style.

The ::first-line invalidation is moved from Element to LayoutObject,
and unnecessary traversal code removed.

I have not been able to come up with a case where we need to compare
PseudoIdFirstLineInherited style, so diffing that is removed.

R=mstensho@opera.com
BUG= 562418 , 564239 , 689979 

Review-Url: https://codereview.chromium.org/2728383002
Cr-Commit-Position: refs/heads/master@{#455088}

[modify] https://crrev.com/3f2d0c6bbce99fc2880356ff2ebfd323b5bcd8bc/third_party/WebKit/LayoutTests/fast/css/invalidation/add-first-line-style-expected.html
[modify] https://crrev.com/3f2d0c6bbce99fc2880356ff2ebfd323b5bcd8bc/third_party/WebKit/LayoutTests/fast/css/invalidation/remove-first-line-style-expected.html
[add] https://crrev.com/3f2d0c6bbce99fc2880356ff2ebfd323b5bcd8bc/third_party/WebKit/LayoutTests/paint/invalidation/first-line-inline-child-expected.html
[add] https://crrev.com/3f2d0c6bbce99fc2880356ff2ebfd323b5bcd8bc/third_party/WebKit/LayoutTests/paint/invalidation/first-line-inline-child.html
[modify] https://crrev.com/3f2d0c6bbce99fc2880356ff2ebfd323b5bcd8bc/third_party/WebKit/Source/core/dom/Element.cpp
[modify] https://crrev.com/3f2d0c6bbce99fc2880356ff2ebfd323b5bcd8bc/third_party/WebKit/Source/core/dom/Element.h
[modify] https://crrev.com/3f2d0c6bbce99fc2880356ff2ebfd323b5bcd8bc/third_party/WebKit/Source/core/layout/LayoutObject.cpp
[modify] https://crrev.com/3f2d0c6bbce99fc2880356ff2ebfd323b5bcd8bc/third_party/WebKit/Source/core/layout/LayoutObject.h