[MediaSession] Add playbackState attribute to Blink MediaSession and use it to determine playback s…

third_party/WebKit/LayoutTests/fast/dom/Window/resources/window-property-collector.js

 function collectProperties(object, windowHasBeenGCed)
 {
     collectPropertiesHelper(object, object, windowHasBeenGCed, []);
 
     propertiesToVerify.sort(function (a, b)
     {
         if (a.property < b.property)
             return -1
         if (a.property > b.property)
             return 1;
@@ skipping 56 matching lines @@
     case "navigator.appName":
     case "navigator.hardwareConcurrency":
     case "navigator.language":
     case "navigator.onLine":
     case "navigator.platform":
     case "navigator.product":
     case "navigator.productSub":
     case "navigator.vendor":
         expected = "window." + propertyPath;
         break;
+    case "navigator.mediaSession.playbackState":
+        expected = "'none'";
+        break;
     case "screen.orientation.type":
         expected = "'portrait-primary'";
         break;
     case "history.scrollRestoration":
         expected = "'auto'";
         break;
     }
 
     insertExpectedResult(path, expected);
 }
@@ skipping 35 matching lines @@
 }
 
 function pathExists(object, path) {
     for (var i = 0; i < path.length; i++) {
         if (!object || !(path[i] in object))
             return false;
         object = object[path[i]];
     }
     return true;
 }