Makes a couple of tests reset state appropriately

Makes a couple of tests reset state appropriately

A couple of tests were setting the ScreenTypeDelegate or Screen during
Setup but never resetting during Teardown. This lead to future tests
failing.

BUG=448189
TEST=covered by tests
R=sadrul@chromium.org

Committed: https://crrev.com/4a193b718a4a09e74ed11f6642e32b55e9e0e955
Cr-Commit-Position: refs/heads/master@{#312268}

[sky, 2015-01-20 17:48:44]

sky@chromium.org changed reviewers:
- jam@chromium.org

[sadrul, 2015-01-20 18:48:14]

LGTM

Would having some ScopedScreenInstall object that sets/unsets things correctly
be less error-prone?

[sky, 2015-01-20 18:56:17]

Definitely. I started going down that route but it started getting rather large
so I settled for this for now.

[sky, 2015-01-20 18:56:21]

The CQ bit was checked by sky@chromium.org

[commit-bot: I haz the power, 2015-01-20 18:58:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/857283002/20001

[commit-bot: I haz the power, 2015-01-20 19:56:04]

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

[commit-bot: I haz the power, 2015-01-20 19:56:05]

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

[sky, 2015-01-20 20:05:42]

The CQ bit was checked by sky@chromium.org

[commit-bot: I haz the power, 2015-01-20 20:06:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/857283002/20001

[commit-bot: I haz the power, 2015-01-20 20:55:06]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-01-20 20:57:16]

Patchset 2 (id:??) landed as
https://crrev.com/4a193b718a4a09e74ed11f6642e32b55e9e0e955
Cr-Commit-Position: refs/heads/master@{#312268}