[eme] Convert lifetime tests to promise_tests

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

Index: third_party/WebKit/LayoutTests/media/encrypted-media/encrypted-media-utils.js
diff --git a/third_party/WebKit/LayoutTests/media/encrypted-media/encrypted-media-utils.js b/third_party/WebKit/LayoutTests/media/encrypted-media/encrypted-media-utils.js
index 3c8cbf9982007769f595a5067d26d3f6f4cb0621..7da412966c110ad85e2eddf65b67ef795f8e3a90 100644
--- a/third_party/WebKit/LayoutTests/media/encrypted-media/encrypted-media-utils.js
+++ b/third_party/WebKit/LayoutTests/media/encrypted-media/encrypted-media-utils.js
@@ -329,3 +329,16 @@ function playVideoAndWaitForTimeupdate(video, content, duration)
         });
     });
 }
+
+// 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:');
+}