[CompositeAfterPaint] Fix crash in PaintLayerPainter::PaintedOutputInvisible()

And unskip media tests. Previously some tests crashed because of the bug.

Bug: 524134
Change-Id: I5f5d71a154468ac7bd64b364b0f0a9a3acd0d6f0
Reviewed-on: https://chromium-review.googlesource.com/c/1383493
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#618982}
3 files changed