Fix CTS test failure due to new PreferenceActivity API in KK

Bug: 10843516
Change-Id: I6479f988a03a2beb697b082a1b8de278431dad4a
diff --git a/tests/tests/preference2/src/android/preference2/cts/PreferenceWithHeaders.java b/tests/tests/preference2/src/android/preference2/cts/PreferenceWithHeaders.java
index 1059700..1bb5637 100644
--- a/tests/tests/preference2/src/android/preference2/cts/PreferenceWithHeaders.java
+++ b/tests/tests/preference2/src/android/preference2/cts/PreferenceWithHeaders.java
@@ -40,6 +40,14 @@
         }
     }
 
+    /*
+     * Validate the fragment loaded into this activity. Required for apps built for API 19 and
+     * above.
+     */
+    protected boolean isValidFragment(String fragment) {
+        return PrefsOneFragment.class.getName().equals(fragment);
+    }
+
     /**
      * Populate the activity with the top-level headers.
      */