[eme] Convert lifetime tests to promise_tests

third_party/WebKit/LayoutTests/media/encrypted-media/encrypted-media-utils.js

 var consoleDiv = null;
 
 function consoleWrite(text)
 {
     if (!consoleDiv && document.body) {
         consoleDiv = document.createElement('div');
         document.body.appendChild(consoleDiv);
     }
     var span = document.createElement('span');
     span.appendChild(document.createTextNode(text));
@@ skipping 311 matching lines @@
     video.play();
     return new Promise(function(resolve) {
         video.addEventListener('timeupdate', function listener(event) {
             if (event.target.currentTime < duration)
                 return;
             video.removeEventListener('timeupdate', listener);
             resolve('success');
         });
     });
 }
+
+// Verifies that the number of existing MediaKey and MediaKeySession objects
+// match what is expected.
+function verifyMediaKeyAndMediaKeySessionCount(
+    expectedMediaKeysCount, expectedMediaKeySessionCount, description)
+{
+    assert_equals(window.internals.mediaKeysCount(),
+                  expectedMediaKeysCount,
+                  description + ', MediaKeys:');
+    assert_equals(window.internals.mediaKeySessionCount(),
+                  expectedMediaKeySessionCount,
+                  description + ', MediaKeySession:');
+}