Add unittests for action_runner.BeginInteraction and action_runner.EndInteraction.

Add unittests for action_runner.BeginInteraction and action_runner.EndInteraction.

This is a reland of https://codereview.chromium.org/294943006 after it's reverted in
https://codereview.chromium.org/284183014/.

BUG=368767
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=272782

[nduca, 2014-05-23 23:21:27]

lgtm

[nednguyen, 2014-05-23 23:21:41]

The CQ bit was checked by nednguyen@google.com

[commit-bot: I haz the power, 2014-05-23 23:23:34]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/nednguyen@google.com/299443017/1

[commit-bot: I haz the power, 2014-05-24 04:53:32]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  mac_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/mac_chromium_rel/buil...)

[commit-bot: I haz the power, 2014-05-24 07:05:44]

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

[commit-bot: I haz the power, 2014-05-24 07:05:44]

Try jobs failed on following builders:
  mac_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/mac_chromium_rel/buil...)

[nednguyen, 2014-05-24 17:55:28]

The CQ bit was checked by nednguyen@google.com

[commit-bot: I haz the power, 2014-05-24 23:19:53]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/nednguyen@google.com/299443017/1

[commit-bot: I haz the power, 2014-05-26 04:13:18]

Change committed as 272782