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
SVN changes up to revision 251550
Eliminate ChromeEncryptor in favor of using webdata's Encryptor directly.

BUG=339731
TEST=chrome, unit_tests, sync_unit_tests
R=zea@chromium.org
TBR=thestig,joi

Review URL: https://codereview.chromium.org/154753004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251551 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251551