"Commit time" data is wrong with UI-side compositing

[Simon Fraser (smfr)]

When web inspecting iOS, or macOS with UI-side compositing enabled, the green "commit time" events in the timeline are always short. I think they only track the time in the fake CA commit triggers in RemoteLayerTreeDrawingArea::displayDidRefresh(), because they are registered like this:


void RemoteLayerTreeDrawingArea::addCommitHandlers()
{
    if (m_webPage.firstFlushAfterCommit())
        return;

    [CATransaction addCommitHandler:[retainedPage = Ref { m_webPage }] {
        if (Page* corePage = retainedPage->corePage()) {
            if (Frame* coreFrame = retainedPage->mainFrame())
                corePage->inspectorController().willComposite(*coreFrame);
        }
    } forPhase:kCATransactionPhasePreLayout];
    
    [CATransaction addCommitHandler:[retainedPage = Ref { m_webPage }] {
        if (Page* corePage = retainedPage->corePage()) {
            if (Frame* coreFrame = retainedPage->mainFrame())
                corePage->inspectorController().didComposite(*coreFrame);
        }
        retainedPage->setFirstFlushAfterCommit(false);
    } forPhase:kCATransactionPhasePostCommit];
    
    m_webPage.setFirstFlushAfterCommit(true);
}

This is wrong because there are no CA Commits (other than this garbage-collection one) in the web process.

[Radar WebKit Bug Importer]

<rdar://problem/103608655>

[Simon Fraser (smfr)]

Bug 249750 fixed this but see also bug 249796.

*** This bug has been marked as a duplicate of bug 249750 ***