[webkit-changes] [WebKit/WebKit] db78f3: Cherry-pick 28c7acb04ba0. rdar://problem/99848107

[Simon Fraser]

  Branch: refs/heads/safari-7615.1.6-branch
  Home:   https://github.com/WebKit/WebKit
  Commit: db78f3693fae15196332ca58261f400dc9704715
      https://github.com/WebKit/WebKit/commit/db78f3693fae15196332ca58261f400dc9704715
  Author: Simon Fraser <simon.fraser at apple.com>
  Date:   2022-09-14 (Wed, 14 Sep 2022)

  Changed paths:
    A LayoutTests/compositing/tiling/sticky-change-to-tiled-expected.html
    A LayoutTests/compositing/tiling/sticky-change-to-tiled.html
    A LayoutTests/compositing/tiling/sticky-with-backdrop-expected.html
    A LayoutTests/compositing/tiling/sticky-with-backdrop.html
    M Source/WebCore/rendering/RenderLayerCompositor.cpp

  Log Message:
  -----------
  Cherry-pick 28c7acb04ba0. rdar://problem/99848107

    REGRESSION (254304 at main): Sidebar on MDN articles is often misplaced
    https://bugs.webkit.org/show_bug.cgi?id=245192
    <rdar://99848107>

    Reviewed by Alan Bujtas and Tim Nguyen.

    For "viewport constrained" scrolling elements, we need to pass the viewportAnchorLayer()
    to the scrolling tree. This happened in the main code path, but this path that
    runs when toggling to/from tiled layers, or with backdrops, also needs updating.

    * LayoutTests/compositing/tiling/sticky-change-to-tiled-expected.html: Added.
    * LayoutTests/compositing/tiling/sticky-change-to-tiled.html: Added.
    * LayoutTests/compositing/tiling/sticky-with-backdrop-expected.html: Added.
    * LayoutTests/compositing/tiling/sticky-with-backdrop.html: Added.
    * Source/WebCore/rendering/RenderLayerCompositor.cpp:
    (WebCore::RenderLayerCompositor::didChangePlatformLayerForLayer):

    Canonical link: https://commits.webkit.org/254496@main

Canonical link: https://commits.webkit.org/254351.4@safari-7615.1.6-branch