reusable public Utterance for a context response when constant size c…

…heckbox changes, see #322

js/view/GFLBScreenView.js

@@ -27,7 +27,7 @@ import ScreenView from '../../../joist/js/ScreenView.js';
 import StringUtils from '../../../phetcommon/js/util/StringUtils.js';
 import ModelViewTransform2 from '../../../phetcommon/js/view/ModelViewTransform2.js';
 import ResetAllButton from '../../../scenery-phet/js/buttons/ResetAllButton.js';
-import { PDOMPeer } from '../../../scenery/js/imports.js';
+import { PDOMPeer, Voicing } from '../../../scenery/js/imports.js';
 import { HBox } from '../../../scenery/js/imports.js';
 import { Node } from '../../../scenery/js/imports.js';
 import { Color } from '../../../scenery/js/imports.js';
@@ -366,6 +366,10 @@ class GFLBScreenView extends ScreenView {
       mass2Node
     ];
 
+    // voicing - Make sure that the Utterances from Alerters only announce when the content under this ScreenView
+    // is visible
+    Voicing.registerUtteranceToNode( alertManager.constantSizeChangedContextResponseUtterance, this );
+
     // layout the view elements
     parameterControlPanel.right = this.layoutBounds.width - 15;
     parameterControlPanel.bottom = MASS_CONTROLS_Y_POSITION;