Fix 5451144: Poking wakelock upon fallback

Now poking the wakelock when Face Unlock goes to the fallback method.
Previously, the backup lock would stay up for a varying amount of
time depending on how long Face Unlock took before fallback.  The
backup is now consistently displayed for 5 seconds.

Also added comments to some older code.

Change-Id: I9f6bdd2d3015e7eb9cb90143737a3cdc87189993

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

@@ -126,6 +126,9 @@ public class LockPatternKeyguardView extends KeyguardViewBase implements Handler
     // The service can take a couple of seconds to start on the first try after boot
     private final int FACELOCK_VIEW_AREA_SERVICE_TIMEOUT = 3000;
 
+    // So the user has a consistent amount of time when brought to the backup method from FaceLock
+    private final int BACKUP_LOCK_TIMEOUT = 5000;
+
     /**
      * The current {@link KeyguardScreen} will use this to communicate back to us.
      */
@@ -587,6 +590,10 @@ public class LockPatternKeyguardView extends KeyguardViewBase implements Handler
 
         if (mLockPatternUtils.usingBiometricWeak() &&
                 mLockPatternUtils.isBiometricWeakInstalled()) {
+            // Note that show() gets called before the screen turns off to set it up for next time
+            // it is turned on.  We don't want to set a timeout on the FaceLock area here because it
+            // may be gone by the time the screen is turned on again.  We set the timout when the
+            // screen turns on instead.
             showFaceLockArea();
         } else {
             hideFaceLockArea();
@@ -1250,6 +1257,7 @@ public class LockPatternKeyguardView extends KeyguardViewBase implements Handler
             if (DEBUG) Log.d(TAG, "FaceLock cancel()");
             hideFaceLockArea(); // Expose fallback
             stopFaceLock();
+            mKeyguardScreenCallback.pokeWakelock(BACKUP_LOCK_TIMEOUT);
         }
 
         // Allows the Face Unlock service to poke the wake lock to keep the lockscreen alive