chromeos::Preferences works correctly in multi-profile session.
* When pref is changed it is applied only if user owning this pref is active.
* Owner's prefernces is saved to local state even if owner is inactive.
Additionally:
* Removed deprecated pref kEnableTouchpadThreeFingerSwipe.
BUG=325564,223480
TEST=browser_tests --gtest_filter=PreferencesTest.*
TBR=noms
Review URL: https://codereview.chromium.org/
142913004
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251550 0039d316-1c4b-4281-b951-d872f2087c98