Add W3C encrypted-media tests

third_party/WebKit/LayoutTests/imported/wpt/encrypted-media/util/testmediasource.js

+function testmediasource(config) {
+
+    return new Promise(function(resolve, reject) {
+        // Fetch the media resources
+        var fetches = [config.audioPath, config.videoPath].map(function(path) {
+            return fetch(path).then(function(response) {
+                if (!response.ok) throw new Error('Resource fetch failed');
+                return response.arrayBuffer();
+            });
+        });
+
+        Promise.all(fetches).then(function(resources) {
+            config.audioMedia = resources[0];
+            config.videoMedia = resources[1];
+
+            // Create media source
+            var source = new MediaSource();
+            source.done = new Promise(function(resolvesource,rejectsource){
+
+                // Create and fill source buffers when the media source is opened
+                source.addEventListener('sourceopen', onSourceOpen);
+                resolve(source);
+
+                function onSourceOpen(event) {
+                    var audioSourceBuffer = source.addSourceBuffer(config.audioType),
+                        videoSourceBuffer = source.addSourceBuffer(config.videoType);
+
+                    audioSourceBuffer.addEventListener('updateend',onUpdateEnd);
+                    videoSourceBuffer.addEventListener('updateend',onUpdateEnd);
+
+                    audioSourceBuffer.appendBuffer(config.audioMedia);
+                    videoSourceBuffer.appendBuffer(config.videoMedia);
+
+                    function onUpdateEnd(event){
+                        event.target.removeEventListener('updateend', onUpdateEnd);
+                        if (!audioSourceBuffer.updating && !videoSourceBuffer.updating) {
+                            if (source.readyState !== 'open') {
+                                rejectsource(new Error("Media source error"));
+                            } else {
+                                source.endOfStream();
+                                resolvesource();
+                            }
+                        }
+                    }
+                }
+            });
+        });
+    });
+}