Re-enabling the OverscrollScreenshot test on ChromeOS while keeping it disabled

Re-enabling the OverscrollScreenshot test on ChromeOS while keeping it disabled
for Ozone. The Ozone flake hasn't been reported on non-ozone trybots.
Created a separate bug for Ozone flake: http://crbug.com/399676 and added some analysis.

BUG=357311
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=287545

[sky, 2014-08-04 17:48:08]

LGTM

[mfomitchev1, 2014-08-04 22:53:33]

The CQ bit was checked by mfomitchev@google.com

[commit-bot: I haz the power, 2014-08-04 22:54:39]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mfomitchev@chromium.org/428303003/1

[commit-bot: I haz the power, 2014-08-05 02:43:29]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_chromium_chromeos_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  win_chromium_x64_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[commit-bot: I haz the power, 2014-08-05 04:51:02]

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

[commit-bot: I haz the power, 2014-08-05 04:51:03]

Try jobs failed on following builders:
  linux_chromium_chromeos_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[mfomitchev, 2014-08-05 14:54:48]

The CQ bit was checked by mfomitchev@chromium.org

[commit-bot: I haz the power, 2014-08-05 14:56:10]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mfomitchev@chromium.org/428303003/1

[commit-bot: I haz the power, 2014-08-05 15:34:32]

Change committed as 287545