Revert 230333 "Processing groups with nextPollSeconds === undefi..."

This may have caused regression on:
http://build.chromium.org/p/chromium.linux/builders/Linux%20Tests/builds/6284

GoogleNowBackgroundUnitTest.ParseAndShowNotificationCardsAdd1Remove1: 
...snip...
Value of: RunJavascriptTestF("GoogleNowBackgroundUnitTest", "ParseAndShowNotificationCardsAdd1Remove1")
Actual: false
Expected: true

> Processing groups with nextPollSeconds === undefined.
> 
> In theory, the server can generate a group with requested == true, but nextPollSeconds === undefined.
> 
> This change makes the client correctly process this.
> 
> BUG=164227
> TEST=No
> 
> Review URL: https://codereview.chromium.org/33433003

TBR=vadimt@chromium.org

Review URL: https://codereview.chromium.org/36583002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230335 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230335