test: Skip fullscreen test on Tizen

This test requires fullscreen support, which is not available on
Tizen.  We should skip the test on any such platform.

This test was passing before the check for fullscreen support was
added to the library to fix #3441.

Change-Id: I6560a919257290540af3ce6a2b3da1a355da9ab9

test/ui/ui_unit.js

@@ -196,6 +196,10 @@ describe('UI', () => {
     });
 
     it('goes into fullscreen on double click', async () => {
+      if (!document.fullscreenEnabled) {
+        pending('This test requires fullscreen support, which is unavailable.');
+      }
+
       const config = {
         controlPanelElements: [
           'overflow_menu',