Exposed current 'timezone' and 'supportedTimezones' valued in chrome.chromeosInfoPrivate.get().
Added chrome.chromeosInfoPrivate.set() method and permitted changing the current 'timezone'.

BUG=313879
TEST=ExtensionApiTest.ChromeOSInfoPrivateTest

Review URL: https://codereview.chromium.org/51343006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232650 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232650