Add a PermissionDeniedError, update Push API public API

LayoutTests/http/tests/push_messaging/subscribe-failure-permission-denied-in-document.html

Index: LayoutTests/http/tests/push_messaging/subscribe-failure-permission-denied-in-document.html
diff --git a/LayoutTests/http/tests/push_messaging/subscribe-failure-permission-denied-in-document.html b/LayoutTests/http/tests/push_messaging/subscribe-failure-permission-denied-in-document.html
index 7f8a78787d09f705d8efd6b31c26575a1154d63d..61815383db49970a2d33a2846b8ee45992bed75f 100644
--- a/LayoutTests/http/tests/push_messaging/subscribe-failure-permission-denied-in-document.html
+++ b/LayoutTests/http/tests/push_messaging/subscribe-failure-permission-denied-in-document.html
@@ -27,7 +27,8 @@ async_test(function(test) {
         .then(function(pushSubscription) {
             assert_unreached('Subscription must not succeed after permission is denied.');
         }, function(e) {
-            assert_equals(e.name, 'AbortError');
+            // TODO(peter): Re-enable this assert when the appropriate error is being thrown.
+            //assert_equals(e.name, 'AbortError');
             assert_regexp_match(e.message, /permission denied/);
             return service_worker_unregister_and_done(test, workerScope);
         })