Fixed flaky fullscreen video test.

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

 var consoleDiv = null;
 var printFullTestDetails = true; // This is optionaly switched of by test whose tested values can differ. (see disableFullTestDetailsPrinting())
 
 logConsole();
 
 if (window.testRunner) {
     if (window.runPixelTests)
         testRunner.dumpAsTextWithPixelResults();
     else
         testRunner.dumpAsText();
@@ skipping 119 matching lines @@
 
 function waitForEventTestAndEnd(element, eventName, testFuncString)
 {
     waitForEventAndTest(element, eventName, testFuncString, true);
 }
 
 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)
 {
     if (success)
         consoleWrite(text + " <span style='color:green'>OK</span>");
     else
         consoleWrite(text + " <span style='color:red'>FAIL</span>");
 }
 
 function consoleWrite(text)
 {
     if (testEnded)
         return;
     logConsole().innerHTML += text + "<br>";
 }