Add test for joint session state manipulation
Browsers don't agree on how top-level container should handle the navigation of the child, particularly around if the state should be overwritten by the child or not.
diff --git a/html/browsers/history/joint-session-history/joint-session-history-iframe-state.html b/html/browsers/history/joint-session-history/joint-session-history-iframe-state.html
new file mode 100644
index 0000000..ffa64c0
--- /dev/null
+++ b/html/browsers/history/joint-session-history/joint-session-history-iframe-state.html
@@ -0,0 +1,41 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>Joint session history should not override parent's state.</title>
+<meta name="timeout" content="long">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+<iframe id="frame" src="about:blank"></iframe>
+<script>
+async_test(function(t) {
+ // Setup.
+ var initialState = {foo: 'bar'};
+ var newStateFromChild = {foo: 'baz'};
+ var child = document.getElementById("frame");
+
+ // Child's initial state should be a default empty state.
+ assert_equals(child.contentWindow.history.state, null);
+
+ // Perform navigation in the top-level container to set the state.
+ window.history.pushState(initialState, 'title');
+
+ // Validate initial state was properly set.
+ assert_object_equals(window.history.state, initialState);
+
+ child.onload = t.step_func_done(() => {
+ // Child's initial state should be `null`.
+ assert_equals(child.contentWindow.history.state, null);
+
+ // Navigate in the child.
+ child.contentWindow.history.pushState(newStateFromChild, 'title');
+
+ // Child's state should now equal the new state.
+ assert_object_equals(child.contentWindow.history.state, newStateFromChild);
+ // Parent's state should still be preserved, having exactly the same state as it
+ // had before parent navigated.
+ assert_object_equals(window.history.state, initialState);
+ })
+ child.src = "joint-session-history-filler.html";
+});
+</script>
+</body>
