Bill McCloskey 8ebd98768a Back out bug 1323207, part 2 - Assert early if we're painting at various points we enter JS (a=backout)
This reverts commit cc6bc31c9f3fb10877292b31c1cf26927856a837.

MozReview-Commit-ID: Dljoh4lYVZ9
2017-01-11 13:20:21 -08:00
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2017-01-08 22:04:19 -06:00