Revert of HelpApp cut at M38: manifest.json

Revert of HelpApp cut at M38: manifest.json (patchset #3 of https://codereview.chromium.org/474223002/)

Reason for revert:
According to Dmitry, we should not use persistent background page.

Original issue's description:
> HelpApp cut at M38: manifest.json
> 
> BUG=chromium:404093
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=290245

TBR=cnwan@google.com,dpolukhin@google.com,nkostylev@chromium.org,dpolukhin@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=chromium:404093
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=290524

[cylee1, 2014-08-19 09:22:12]

Created Revert of HelpApp cut at M38: manifest.json

[commit-bot: I haz the power, 2014-08-19 09:22:55]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/cylee@chromium.org/470313003/1

[commit-bot: I haz the power, 2014-08-19 09:22:57]

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

[commit-bot: I haz the power, 2014-08-19 09:22:58]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[cylee1, 2014-08-19 09:23:49]

Hi Dmitry, committer approval needed. thanks.

[Dmitry Polukhin, 2014-08-19 09:24:22]

lgtm

[cylee1, 2014-08-19 09:28:49]

The CQ bit was checked by cylee@chromium.org

[commit-bot: I haz the power, 2014-08-19 09:30:11]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/cylee@chromium.org/470313003/1

[commit-bot: I haz the power, 2014-08-19 09:31:48]

Committed patchset #1 (1) as 290524