Added UMA metrics for ChromeOS first-run UI.

Added following metrics:
 * CrosFirstRun.DialogShown
 * CrosFirstRun.FurthestStep
 * CrosFirstRun.TimeSpent
 * CrosFirstRun.TimeSpentOnStepAppList
 * CrosFirstRun.TimeSpentOnStepHelp
 * CrosFirstRun.TimeSpentOnStepTray
 * CrosFirstRun.TutorialCompletion
 * CrosFirstRun.TutorialLaunched

BUG=269291

Review URL: https://codereview.chromium.org/131023003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245212 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245212