[Cairo] Cairo graphics backend uses ImageBuffer::copyImage just to access native image buffer handles

[Chris Lord]

This pattern occurs a lot in the Cairo graphics backend:

    RefPtr<Image> image = layerImage.copyImage(DontCopyBackingStore);
    if (!image)
        return;

    if (auto surface = image->nativeImageForCurrentFrame()) {
        ...
    }

Which is fine on a single thread, but ImageSource is not usable off-main-thread, so any drawing that calls functions that do this will cause an assert on a debug build. I think its use of ImageSource would be safe off-main-thread, but it's overkill just to get the native image handle. This is hampering OffscreenCanvas.

[Chris Lord]

Created attachment 382908 [details]
Patch

[WebKit Commit Bot]

Comment on attachment 382908 [details]
Patch

Clearing flags on attachment: 382908

Committed r252136: <https://trac.webkit.org/changeset/252136>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.

[Radar WebKit Bug Importer]

<rdar://problem/56940631>