Element#innerText ignores text-transform in ::first-line

Demo: https://jsfiddle.net/k1pgLb9x/2/
<style>
p::first-line { text-transform: uppercase }
</style>
<p>abc<br>def</p>
document.querySelector('p') should be "ABC\ndef" but got "abc\ndef"
for both legacy layout and LayoutNG