Adding info explaining facelock's backup lock

This changes the security picker when selecting a backup lock for facelock
such that it says back up lock and gives a brief description of why it's needed.
This is currently a temporary way to display the info and will need to be changed
for the final release.

Change-Id: I6373f97caec088482d36c65bd210c79238c623cf

res/values/strings.xml

@@ -756,6 +756,9 @@
     <!--  Title for security picker to choose the unlock method: None/Pattern/PIN/Password [CHAR LIMIT=22] -->
     <string name="lock_settings_picker_title">Screen lock</string>
 
+    <!--  Title for security picker when choosing a facelock's backup unlock method: Pattern/PIN [CHAR LIMIT=22] -->
+    <string name="backup_lock_settings_picker_title">Choose backup lock</string>
+
     <!--  Main Security lock settings --><skip />
     <!--  Title for PreferenceScreen to launch picker for security method when there is none [CHAR LIMIT=22] -->
     <string name="unlock_set_unlock_launch_picker_title">Screen lock</string>
@@ -769,6 +772,9 @@
     <!--  Summary for PreferenceScreen to changeecurity method: None/Pattern/PIN/Password [CHAR LIMIT=45]  -->
     <string name="unlock_set_unlock_launch_picker_enable_summary">Choose a method to lock the screen</string>
 
+    <!-- Info explaining the backup lock which is used for facelock -->
+    <string name="unlock_backup_info_summary">When conditions for FaceLock aren\'t ideal, how do you want to unlock?</string>
+
     <!-- Title for preference that disables unlock security [CHAR LIMIT=22] -->
     <string name="unlock_set_unlock_off_title">None</string>
     <!-- Summary for preference that disables unlock security [CHAR LIMIT=45] -->

res/xml/security_settings_picker.xml

@@ -20,6 +20,13 @@
         android:key="security_picker_category"
         android:title="@string/lock_settings_picker_title">
 
+<!-- TODO: find a better way to display this backup info -->
+        <PreferenceScreen
+            android:key="unlock_backup_info"
+            android:summary="@string/unlock_backup_info_summary"
+            android:selectable="false"
+            android:persistent="false"/>
+
         <PreferenceScreen
             android:key="unlock_set_off"
             android:title="@string/unlock_set_unlock_off_title"

src/com/android/settings/ChooseLockGeneric.java

@@ -43,6 +43,7 @@ public class ChooseLockGeneric extends PreferenceActivity {
 
     public static class ChooseLockGenericFragment extends SettingsPreferenceFragment {
         private static final int MIN_PASSWORD_LENGTH = 4;
+        private static final String KEY_UNLOCK_BACKUP_INFO = "unlock_backup_info";
         private static final String KEY_UNLOCK_SET_OFF = "unlock_set_off";
         private static final String KEY_UNLOCK_SET_NONE = "unlock_set_none";
         private static final String KEY_UNLOCK_SET_BIOMETRIC_WEAK = "unlock_set_biometric_weak";
@@ -212,13 +213,21 @@ public class ChooseLockGeneric extends PreferenceActivity {
                     .getBooleanExtra(LockPatternUtils.LOCKSCREEN_BIOMETRIC_WEAK_FALLBACK, false);
             final boolean weakBiometricAvailable = isBiometricSensorAvailable(
                     DevicePolicyManager.PASSWORD_QUALITY_BIOMETRIC_WEAK);
+            if (onlyShowFallback) {
+                picker.setTitle(R.string.backup_lock_settings_picker_title);
+            } else {
+                picker.setTitle(R.string.lock_settings_picker_title);
+            }
             for (int i = preferenceCount-1; i >= 0; --i) {
                 Preference pref = cat.getPreference(i);
                 if (pref instanceof PreferenceScreen) {
                     final String key = ((PreferenceScreen) pref).getKey();
                     boolean enabled = true;
                     boolean visible = true;
-                    if (KEY_UNLOCK_SET_OFF.equals(key)) {
+                    if (KEY_UNLOCK_BACKUP_INFO.equals(key)) {
+                        enabled = true;
+                        visible = onlyShowFallback;
+                    } else if (KEY_UNLOCK_SET_OFF.equals(key)) {
                         enabled = quality <= DevicePolicyManager.PASSWORD_QUALITY_UNSPECIFIED;
                     } else if (KEY_UNLOCK_SET_NONE.equals(key)) {
                         enabled = quality <= DevicePolicyManager.PASSWORD_QUALITY_UNSPECIFIED;
@@ -250,7 +259,8 @@ public class ChooseLockGeneric extends PreferenceActivity {
          * @return true if allowed
          */
         private boolean allowedForFallback(String key) {
-            return KEY_UNLOCK_SET_PATTERN.equals(key) || KEY_UNLOCK_SET_PIN.equals(key);
+            return KEY_UNLOCK_BACKUP_INFO.equals(key)  ||
+                    KEY_UNLOCK_SET_PATTERN.equals(key) || KEY_UNLOCK_SET_PIN.equals(key);
         }
 
         private boolean isBiometricSensorAvailable(int quality) {