Always disable() through SBMS; watch date.

Touching StatusBar.disable() directly can make the cached value over
in StatusBarManagerService stale.  Instead, dispatch DISABLE_BACK
through setSystemUiVisibility() on tablets; it's unused on phones.

Also DISABLE_NOTIFICATION_TICKER when showing secure lockscreen, and
watch for TIME_CHANGED in DateView.

Bug: 5255469
Bug: 5242677
Change-Id: I4efaf9799b2f229f49d7024da5dafceacd5e08bb

services/java/com/android/server/StatusBarManagerService.java

@@ -301,7 +301,7 @@ public class StatusBarManagerService extends IStatusBarService.Stub
         // also allows calls from window manager which is in this process.
         enforceStatusBarService();
 
-        if (SPEW) Slog.d(TAG, "setSystemUiVisibility(" + vis + ")");
+        if (SPEW) Slog.d(TAG, "setSystemUiVisibility(0x" + Integer.toHexString(vis) + ")");
 
         synchronized (mLock) {
             updateUiVisibilityLocked(vis);