Add tests while FullscreenUnprefixed flag is turned off.

third_party/WebKit/LayoutTests/shadow-dom/fullscreen-element-in-shadow-complex.html

Index: third_party/WebKit/LayoutTests/shadow-dom/fullscreen-element-in-shadow-complex.html
diff --git a/third_party/WebKit/LayoutTests/shadow-dom/fullscreen-element-in-shadow-complex.html b/third_party/WebKit/LayoutTests/shadow-dom/fullscreen-element-in-shadow-complex.html
index 1613df980ad9669fd2104eeca772c59695e114f9..f6423f918d47266484c50820f78b376e3d797066 100644
--- a/third_party/WebKit/LayoutTests/shadow-dom/fullscreen-element-in-shadow-complex.html
+++ b/third_party/WebKit/LayoutTests/shadow-dom/fullscreen-element-in-shadow-complex.html
@@ -67,6 +67,15 @@ async_test((test) => {
         assert_equals(host4.shadowRoot.fullscreenElement, null);
         assert_equals(host5.shadowRoot.fullscreenElement, null);
 
+        // TODO(kochi): The 'retargeting' behavior is controlled by
+        // 'FullscreenUnprefixed' runtime flag dynamically.  Until the
+        // flag is turned on, document.webkitFullscreenElement leaks the
+        // fullscreen element under shadow roots.
+        window.internals.runtimeFlags.fullscreenUnprefixedEnabled = false;
+        assert_false(window.internals.runtimeFlags.fullscreenUnprefixedEnabled);
+        assert_equals(document.webkitFullscreenElement, canvas);
+        assert_equals(document.webkitCurrentFullScreenElement, canvas);
+
         document.exitFullscreen();
         test.done();
     });