Remove windows.onCreated hack from Keep Awake extension.

Remove windows.onCreated hack from Keep Awake extension.

The example extension for the chrome.power API registered a
listener for windows.onCreated to work around an issue where
runtime.onStartup didn't fire on Chrome OS. The underlying
Chrome bug has been fixed now, so the windows.onCreated
workaround is no longer needed.

BUG=222473
TEST=install the extension on Chrome OS and check that
     /var/log/power_manager/powerd.LATEST reports an
     extension-driven policy change when logging in

Committed: https://crrev.com/3d20816f65b5b9f25e194ef725b94157bf2b1533
Cr-Commit-Position: refs/heads/master@{#293043}

[Daniel Erat, 2014-09-02 21:18:15]

derat@chromium.org changed reviewers:
+ rockot@chromium.org

[Ken Rockot(use gerrit already), 2014-09-02 22:53:28]

lgtm

[Daniel Erat, 2014-09-02 22:54:38]

The CQ bit was checked by derat@chromium.org

[commit-bot: I haz the power, 2014-09-02 23:11:59]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/derat@chromium.org/531953002/1

[commit-bot: I haz the power, 2014-09-03 01:42:50]

Committed patchset #1 (id:1) as ad0b6482455c6dba6aa115bfbc7afb407237b19e

[commit-bot: I haz the power, 2014-09-10 03:22:38]

Patchset 1 (id:??) landed as
https://crrev.com/3d20816f65b5b9f25e194ef725b94157bf2b1533
Cr-Commit-Position: refs/heads/master@{#293043}