Added callback to allow Face Unlock to hide black area

- Part of fix 5491362 (RelTeamHotIssue)

- Because the fix closes the camera early, this change is needed so
  the black area isn't still hanging around while the camera fades
  to the backup lock.

Change-Id: Iab7c264adab0fb05979fe2732048ccf2237e64c5

Author: Brian Colonna

core/java/com/android/internal/policy/IFaceLockCallback.aidl

@@ -22,5 +22,6 @@ oneway interface IFaceLockCallback {
     void unlock();
     void cancel();
     void reportFailedAttempt();
+    void exposeFallback();
     void pokeWakelock();
 }

policy/src/com/android/internal/policy/impl/LockPatternKeyguardView.java

@@ -1375,6 +1375,13 @@ public void reportFailedAttempt() {
             mKeyguardScreenCallback.pokeWakelock(BACKUP_LOCK_TIMEOUT);
         }
 
+        // Removes the black area that covers the backup unlock method
+        @Override
+        public void exposeFallback() {
+            if (DEBUG) Log.d(TAG, "FaceLock exposeFallback()");
+            hideFaceLockArea(); // Expose fallback
+        }
+
         // Allows the Face Unlock service to poke the wake lock to keep the lockscreen alive
         @Override
         public void pokeWakelock() {