Add tests for removing the parent/child of the fullscreen element

LayoutTests/fullscreen/api/element-request-fullscreen-top.html

Index: LayoutTests/fullscreen/api/element-request-fullscreen-top.html
diff --git a/LayoutTests/fullscreen/api/element-request-fullscreen-top.html b/LayoutTests/fullscreen/api/element-request-fullscreen-top.html
index 36cb40f53e6f74a190b2cba22cdd645297d3b5a9..260b8631902995ddbb102d3a42eeae1aa04827e1 100644
--- a/LayoutTests/fullscreen/api/element-request-fullscreen-top.html
+++ b/LayoutTests/fullscreen/api/element-request-fullscreen-top.html
@@ -17,7 +17,7 @@ async_test(function(t)
         trusted_event(t.step_func(function()
         {
             top.requestFullscreen();
-            // An fullscreenerror event would be fired after an async section
+            // A fullscreenerror event would be fired after an async section
             // and an animation frame task, so wait until after that.
             setTimeout(requestAnimationFrame.bind(null, t.step_func_done()), 0);
         }), top);