Convert \n in browser designer page (#1944)

Change-Id: Iffc170ed207d6325663fafc25c4d19fef7dbd4bf
Co-authored-by: Evan W. Patton <ewpatton@mit.edu>

appinventor/appengine/src/com/google/appinventor/client/editor/simple/components/MockLabel.java

@@ -25,7 +25,7 @@ public final class MockLabel extends MockVisibleComponent {
   // GWT label widget used to mock a Simple Label
   private InlineHTML labelWidget;
 
-  private String savedText;     // Saved text, so if we change from
+  private String savedText = "";     // Saved text, so if we change from
                                      // text to/from html we have the text
                                      // to set
 
@@ -100,9 +100,15 @@ public final class MockLabel extends MockVisibleComponent {
   private void setTextProperty(String text) {
     savedText = text;
     if (getPropertyValue(PROPERTY_NAME_HTMLFORMAT).equals("True")) {
-      labelWidget.setHTML(SimpleHtmlSanitizer.sanitizeHtml(text).asString());
+      String sanitizedText = SimpleHtmlSanitizer.sanitizeHtml(text).asString();
+      if (sanitizedText != null) {
+        sanitizedText = sanitizedText.replaceAll("\\\\n", " ");
+      }
+      labelWidget.setHTML(sanitizedText);
     } else {
-      labelWidget.setText(text);
+      labelWidget.setHTML(text.replaceAll("&", "&amp;").replaceAll("<", "&lt;")
+          .replaceAll(">", "&gt;").replaceAll("\\\\n", "<br>")
+      );
     }
   }