Add priority to Notification & NotificationOptions.

LayoutTests/http/tests/notifications/serviceworker-notificationclick-event-reflection.html

Index: LayoutTests/http/tests/notifications/serviceworker-notificationclick-event-reflection.html
diff --git a/LayoutTests/http/tests/notifications/serviceworker-notificationclick-event-reflection.html b/LayoutTests/http/tests/notifications/serviceworker-notificationclick-event-reflection.html
index ad8f02c5f3871e58fabc955178b7a51ec872a645..73c7ef1aac139e3d3eee5d1692c485992ed1192e 100644
--- a/LayoutTests/http/tests/notifications/serviceworker-notificationclick-event-reflection.html
+++ b/LayoutTests/http/tests/notifications/serviceworker-notificationclick-event-reflection.html
@@ -23,6 +23,7 @@
               lang: 'nl-NL',
               body: 'Hello, world!',
               tag: 'tag',
+              priority: 'high',
               // FIXME: Relative URLs for the icon attribute currently get reflected as
               // an absolute URL, which should probably be the given relative URL.
               icon: 'https://example/icon.png',
@@ -69,6 +70,10 @@
                   assert_equals(event.data.command, 'click', 'The notification was expected to be clicked.');
 
                   Object.keys(options).forEach(function(key) {
+                      if (key == 'priority') {
+                          // TODO(johnme): priority is not yet serialized properly.
+                          return;
+                      }
                       if (key == 'actions') {
                           // TODO(johnme): actions are not yet serialized properly.
                           return;