Use event init dictionaries in modules/{notifications,push_messaging,serviceworkers}

LayoutTests/http/tests/push_messaging/resources/pushevent-extendable-event.js

 importScripts('../../serviceworker/resources/worker-testharness.js');
 importScripts('/resources/testharness-helpers.js');
 
 test(function() {
     assert_true('PushEvent' in self);
 
     var event = new PushEvent('PushEvent');
     assert_equals(event.type, 'PushEvent');
     assert_own_property(event, 'data');
+    assert_equals(event.cancelable, false);
+    assert_equals(event.bubbles, false);
     assert_inherits(event, 'waitUntil');
 
+    var data = new PushMessageData('foo');
+    var eventWithInit = new PushEvent('PushEvent',
+                                      { cancelable: true,
+                                        bubbles: true,
+                                        data: data,
+                                      });
+    assert_equals(eventWithInit.cancelable, true);
+    assert_equals(eventWithInit.bubbles, true);
+    assert_equals(eventWithInit.data, data);
+
 }, 'PushEvent is exposed and extends ExtendableEvent.');