Don't commit prefs::kStabilitySessionEndCompleted change immediately on chromeos
 Chrome on ChromeOS gets killed and generate dump when hangs or didn't respond in time, so this isn't necessary.

BUG=302578

Review URL: https://codereview.chromium.org/25484004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229535 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229535