[Webkit-unassigned] [Bug 170113] New: ASSERT(!needsLayout()) in FrameView::paintContents() when setting a CSS class during handling of a "loadedmetadata" event

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=170113

            Bug ID: 170113
           Summary: ASSERT(!needsLayout()) in FrameView::paintContents()
                    when setting a CSS class during handling of a
                    "loadedmetadata" event
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: graouts at apple.com
                CC: bfulgham at webkit.org, simon.fraser at apple.com,
                    zalan at apple.com

A previous version of the patch for https://bugs.webkit.org/show_bug.cgi?id=169145 would infrequently hit `ASSERT(!needsLayout())` in FrameView::paintContents(). This was due to those three lines in _mediaDocumentHasMetadata() in Source/WebCore/Modules/modern-media-controls/media/media-document-controller.js:

    const media = this.mediaController.media;
    media.classList.add(this.mediaController.isAudio ? "audio" : "video");
    media.classList.add(window.navigator.platform === "MacIntel" ? "mac" : window.navigator.platform);

This code is called as a result of handling a "loadedmetadata" event, which is fired asynchronously. You can re-create the assertion by removing the enclosing requestAnimationFrame() call and running this command:

    run-webkit-tests --debug -1 --iterations=500 --exit-after-n-failures=1 fast/events/media-focus-in-standalone-media-document.html

You should see DRT crash relatively quickly as this ASSERT is hit.

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