Fixed flaky fullscreen video test.

third_party/WebKit/LayoutTests/fullscreen/full-screen-test.js

Index: third_party/WebKit/LayoutTests/fullscreen/full-screen-test.js
diff --git a/third_party/WebKit/LayoutTests/fullscreen/full-screen-test.js b/third_party/WebKit/LayoutTests/fullscreen/full-screen-test.js
index ae6ff349b2ed3c32f5b68d4b987a8a10b60c6780..29484405ea3f9f0a5a019dce1046783ad28254ec 100644
--- a/third_party/WebKit/LayoutTests/fullscreen/full-screen-test.js
+++ b/third_party/WebKit/LayoutTests/fullscreen/full-screen-test.js
@@ -137,10 +137,12 @@ var testEnded = false;
 
 function endTest()
 {
+    if (testEnded)
+        return;
     consoleWrite("END OF TEST");
     testEnded = true;
     if (window.testRunner)
-        testRunner.notifyDone();
+        testRunner.layoutAndPaintAsyncThen(() => testRunner.notifyDone());
 }
 
 function logResult(success, text)