Sync "fully exit fullscreen" with the spec

LayoutTests/fullscreen/model/fully-exit-fullscreen.js

Index: LayoutTests/fullscreen/model/fully-exit-fullscreen.js
diff --git a/LayoutTests/fullscreen/model/fully-exit-fullscreen.js b/LayoutTests/fullscreen/model/fully-exit-fullscreen.js
new file mode 100644
index 0000000000000000000000000000000000000000..9cfb0058202b4a4bdfb4e86eceae5fd887dbdac7
--- /dev/null
+++ b/LayoutTests/fullscreen/model/fully-exit-fullscreen.js
@@ -0,0 +1,8 @@
+// Invokes "fully exit fullscreen" for document.
+function fully_exit_fullscreen(document)
+{
+    // FIXME: window.open() invokes "fully exit fullscreen", but the HTML spec
+    // doesn't say so, and none of the spec'd behavior is implemented:
+    // https://www.w3.org/Bugs/Public/show_bug.cgi?id=26584
+    document.defaultView.open("data:text/html,<script>window.close()</script>");
+}