Announce dynamic content changes in lock confirmation settings.

Also re-orders updateStage() and setText/Selection calls so that text
events don't flush announcements. This does not change functionality.

Bug: 7256500
Change-Id: I8b10d66e9f73c7a630a8c3c5128372e18f26234c

src/com/android/settings/ChooseLockPattern.java

@@ -429,6 +429,7 @@ public class ChooseLockPattern extends PreferenceActivity {
          * @param stage
          */
         protected void updateStage(Stage stage) {
+            final Stage previousStage = mUiStage;
 
             mUiStage = stage;
 
@@ -493,6 +494,12 @@ public class ChooseLockPattern extends PreferenceActivity {
                 case ChoiceConfirmed:
                     break;
             }
+
+            // If the stage changed, announce the header for accessibility. This
+            // is a no-op when accessibility is disabled.
+            if (previousStage != stage) {
+                mHeaderText.announceForAccessibility(mHeaderText.getText());
+            }
         }