Fix a race - synchronize test completion with media's loadstart event.

Presence of OOPIFs introduces a delay into loading of cross-origin media and
exposes a race in the
http/tests/security/mixedContent/insecure-audio-video-in-main-frame.html
test.  To get rid of the race, we should wait until media has actually
started to load, before posting / reporting that the test is "done".

BUG=582541
TEST=The affected test passes when run 100 times with and without --site-per-process flag.

Review URL: https://codereview.chromium.org/1703333002

Cr-Commit-Position: refs/heads/master@{#376065}

third_party/WebKit/LayoutTests/FlagExpectations/site-per-process

@@ -78,9 +78,6 @@ http/tests/security/xssAuditor/full-block-script-tag-cross-domain.html [ Failure
 http/tests/security/xssAuditor/full-block-post-from-iframe.html [ Failure ]
 http/tests/security/xssAuditor/xss-protection-parsing-01.html [ Failure ]
 
-# https://crbug.com/582541 - MixedContentChecker::shouldBlockFetch returns false with --site-per-process
-http/tests/security/mixedContent/insecure-audio-video-in-main-frame.html [ Failure ]
-
 # https://crbug.com/582522 - extra mixedContent checks reported with --site-per-process
 http/tests/security/mixedContent/insecure-iframe-in-iframe.html [ Failure ]
 

third_party/WebKit/LayoutTests/http/tests/security/mixedContent/resources/frame-with-insecure-audio-video.html

@@ -3,13 +3,31 @@
 <video></video>
 <script>
     window.addEventListener('load', function () {
+        var windowOpener = window.opener;
+        var isAudioLoaded = false;
+        var isVideoLoaded = false;
+        function checkTestCompletion() {
+          if (isAudioLoaded && isVideoLoaded && windowOpener) {
+            windowOpener.postMessage('done', '*');
+          }
+        }
+
         // Assigning via JavaScript after 'load' rather than direclty in the
         // markup in order to avoid the console's flaky "what line am I on?"
         // autodetection.
-        document.querySelector('audio').src = "http://127.0.0.1:8080/resources/test.mp4";
-        document.querySelector('video').src = "http://127.0.0.1:8080/resources/test.mp4";
-        if (window.opener)
-            window.opener.postMessage('done', '*');
+        var audioElement = document.querySelector('audio');
+        audioElement.src = "http://127.0.0.1:8080/resources/test.mp4";
+        audioElement.addEventListener("loadstart", function(event) {
+          isAudioLoaded = true;
+          checkTestCompletion();
+        });
+
+        var videoElement = document.querySelector('video');
+        videoElement.src = "http://127.0.0.1:8080/resources/test.mp4";
+        videoElement.addEventListener("loadstart", function(event) {
+          isVideoLoaded = true;
+          checkTestCompletion();
+        });
     });
 </script>
 </body>