Set the NavigationApi state object during commit, rather than after

Spec: WICG/navigation-api#236

Bug: 1183545

Change-Id: I203419f45a3dfba1b4dab3dc2672146b2da92ce3

navigation-api/state/same-document-away-and-back-navigation-api.html

@@ -36,7 +36,7 @@
       assert_equals(state2.statevar, "state");
       assert_equals(state2.startvar2, "otherstate");
 
-      history.back();
+      navigation.back();
       window.onpopstate = t.step_func_done(() => {
         assert_equals(navigation.entries().length, 3);
         let back_entry = navigation.currentEntry;