Move some paint-related tests to NeverFixTests

The moved tests are always expected to fail due to stack-space issues
or incompatible test flags. Also update the comment as to what belongs
in NeverFixTests.

Two tests that were in NeverFixTests are just Slow now, so re-enable them.

R=dpranke@chromium.org
BUG=381840,601669,646528

Review-Url: https://codereview.chromium.org/2334893002
Cr-Commit-Position: refs/heads/master@{#418862}
18 files changed