Add W3C encrypted-media tests

third_party/WebKit/LayoutTests/imported/wpt/encrypted-media/scripts/setmediakeys-at-same-time.js

+function runTest(config, qualifier) {
+    var testname = testnamePrefix(qualifier, config.keysystem)
+                                             + ', setmediakeys at same time';
+
+    var configuration = getSimpleConfigurationForContent(config.content);
+
+    async_test(function(test) {
+        var _video = config.video,
+            _access,
+            _mediaKeys1,
+            _mediaKeys2,
+            _mediaKeys3,
+            _mediaKeys4,
+            _mediaKeys5;
+
+        // Test MediaKeys assignment.
+        assert_equals(_video.mediaKeys, null);
+        assert_equals(typeof _video.setMediaKeys, 'function');
+
+        function onFailure(error) {
+            forceTestFailureFromPromise(test, error);
+        }
+
+        function setMediaKeys(mediaKeys) {
+            return _video.setMediaKeys(mediaKeys)
+                .then(function() {return 1}, function() {return 0})
+        }
+
+        navigator.requestMediaKeySystemAccess(config.keysystem, [configuration]).then(function(access) {
+            _access = access;
+            return _access.createMediaKeys();
+        }).then(function(result) {
+            _mediaKeys1 = result;
+            return _access.createMediaKeys();
+        }).then(function(result) {
+            _mediaKeys2 = result;
+            return _access.createMediaKeys();
+        }).then(function(result) {
+            _mediaKeys3 = result;
+            return _access.createMediaKeys();
+        }).then(function(result) {
+            _mediaKeys4 = result;
+            return _access.createMediaKeys();
+        }).then(function(result) {
+            _mediaKeys5 = result;
+            return Promise.all([
+                setMediaKeys(_mediaKeys1),
+                setMediaKeys(_mediaKeys2),
+                setMediaKeys(_mediaKeys3),
+                setMediaKeys(_mediaKeys4),
+                setMediaKeys(_mediaKeys5)
+            ]);
+        }).then(function(results) {
+            var sum = results.reduce((a, b) => a + b, 0);
+            assert_in_array(sum,[1,5]);
+            test.done();
+        }).catch(onFailure);
+    }, testname);
+}