Seeing http://build.chromium.org/p/chromium.webkit/builders/GPU%20Mac%20%28dbg%29/builds/9209, r130994 broke the chromium test.
This assertion fires because there is a built-in assumption that 2d canvas operations are always triggered from within a WebThread task. This test appears to be an exception to that assumption.
Created attachment 168225 [details] Patch
Comment on attachment 168225 [details] Patch OK. r=me
Comment on attachment 168225 [details] Patch Clearing flags on attachment: 168225 Committed r131059: <http://trac.webkit.org/changeset/131059>
All reviewed patches have been landed. Closing bug.