[webkit-changes] [WebKit/WebKit] 0d8538: REGRESSION(257456 at main): Scrollbar shows up on sit...

[Tim Nguyen]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: 0d8538115ee0a3fb26afd3e5d3a2fd1f9291d1c3
      https://github.com/WebKit/WebKit/commit/0d8538115ee0a3fb26afd3e5d3a2fd1f9291d1c3
  Author: Tim Nguyen <ntim at apple.com>
  Date:   2023-07-26 (Wed, 26 Jul 2023)

  Changed paths:
    A LayoutTests/fullscreen/fullscreen-no-scrollbars-on-ancestor-root-expected.html
    A LayoutTests/fullscreen/fullscreen-no-scrollbars-on-ancestor-root.html
    M Source/WebCore/css/SelectorCheckerTestFunctions.h

  Log Message:
  -----------
  REGRESSION(257456 at main): Scrollbar shows up on sites that initiate fullscreen from an iframe
https://bugs.webkit.org/show_bug.cgi?id=255197
rdar://108096981

Reviewed by Simon Fraser.

The following UA stylesheet rule was not applying:
```
:root:-webkit-full-screen-document:not(:fullscreen) {
    overflow: hidden !important;
}
```
because :-webkit-full-screen-document used isFullscreen() (exposed as a legacy API), did not take in account documents fullscreened implicitly by their child frame.

Switch to fullscreenElement() which queries from the top layer, and includes implicitly fullscreened elements.

* LayoutTests/fullscreen/fullscreen-no-scrollbars-on-ancestor-root-expected.html: Added.
* LayoutTests/fullscreen/fullscreen-no-scrollbars-on-ancestor-root.html: Added.
* Source/WebCore/css/SelectorCheckerTestFunctions.h:
(WebCore::matchesFullScreenDocumentPseudoClass):

Canonical link: https://commits.webkit.org/266340@main