[Webkit-unassigned] [Bug 256262] New: HTMLCanvasElement is orphaned causing a HTMLDocument leak on YouTube video pages

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=256262

            Bug ID: 256262
           Summary: HTMLCanvasElement is orphaned causing a HTMLDocument
                    leak on YouTube video pages
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Canvas
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: rreno at apple.com
                CC: dino at apple.com, webkit-bug-importer at group.apple.com

See also https://webkit.org/b/251835

Quoting Simon from that bug:
>Launch a recent Safari or MiniBrowser build from terminal (so you can see the output), and visit a YouTube.com video page (or a page with YouTube.com in a subframe). In that tab, navigate to about:blank, then trigger the low memory >handler (to clear caches):
>> notifyutil -p "org.WebKit.lowMemory"
>
>then dump the list of live documents:
>> notifyutil -p  "com.apple.WebKit.showAllDocuments"

As of 263633 at main you will likely see the YouTube document with ref count > 10 and referencingNodeCount anywhere from about 7500 - 15000 depending on when you navigated away from the page. If you apply the patch in the PR in 251835 then you will see the HTMLDocument has refCount 0 and referencingNodeCount 1. That 1 node is an HTMLCanvasElement.

>From preliminary testing (adding Ref tracking to HTMLCanvasElement and to the Node ctor and dtors) it appears the pointer to the element may have been leaked from the smart pointer and never derefed.

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