MSE: Unhide potential flakiness in duration and redundant seek tests

MSE: Unhide potential flakiness in duration and redundant seek tests

This CL fixes the hiding of potential real flakiness for two MSE layout
tests. These two tests are guaranteed to fail since their expectations
were not updated along with Blink r195852 (which changed how
testharness-js reports are generated and compared). Any that all PASS no
longer need an explicit expectation. If there is an explicit expectation
for a testharness-js layout test, it needs some additional header and
footer.  Since both of these tests should succeed (though might be flaky
still), this change removes their explicit PASS expectation files.

BUG=418324, 309184, 303419, 284782
R=tkent@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=196414

[wolenetz, 2015-06-03 03:53:12]

The CQ bit was checked by wolenetz@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-06-03 03:53:27]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1147263005/1

[wolenetz, 2015-06-03 03:53:44]

Please take a look at patch set 1. I'd like to fix the real flakiness, but it's
hiding from me :)

Thanks!
Matt

[tkent, 2015-06-03 03:57:50]

lgtm

[commit-bot: I haz the power, 2015-06-03 06:52:02]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-06-03 06:52:03]

Dry run: Try jobs failed on following builders:
  win_blink_rel on tryserver.blink (JOB_FAILED,
http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/64934)

[wolenetz, 2015-06-03 15:35:07]

The CQ bit was checked by wolenetz@chromium.org

[commit-bot: I haz the power, 2015-06-03 15:35:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1147263005/1

[commit-bot: I haz the power, 2015-06-03 16:33:43]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=196414