Assert history.state does not get serialized and deserialized during …

…bfcache navigation

See whatwg/html#6652.

html/browsers/history/the-history-interface/history-state-after-bfcache.window.js

@@ -0,0 +1,39 @@
+// META: title=Navigating back to a bfcached page does not reset history.state
+// META: script=/common/dispatcher/dispatcher.js
+// META: script=/common/utils.js
+// META: script=/html/browsers/browsing-the-web/remote-context-helper/resources/remote-context-helper.js
+
+// See https://github.com/whatwg/html/issues/6652.
+
+'use strict';
+
+promise_test(async t => {
+  const rcHelper = new RemoteContextHelper();
+
+  // Open a window with noopener so that BFCache will work.
+  const rc = await rcHelper.addWindow(null, { features: "noopener" });
+
+  // Add a pageshow listener to stash the event, and set history.state using replaceState().
+  await rc.executeScript(() => {
+    window.addEventListener('pageshow', (event) => {
+      window.pageshowEvent = event;
+    });
+
+    history.replaceState({ foo: 'bar' }, '', '');
+    window.stashedHistoryState = history.state;
+  });
+
+  const rc2 = await rc.navigateToNew();
+  await rc2.historyBack();
+
+  assert_implements_optional(
+    await rc.executeScript(() => window.pageshowEvent.persisted),
+    'precondition: document was bfcached'
+  );
+
+  assert_equals(await rc.executeScript(() => history.state.foo), 'bar', 'history.state was restored correctly');
+
+  assert_true(
+    await rc.executeScript(() => window.stashedHistoryState === history.state),
+    'history.state did not get serialized and deserialized');
+});