blink: Add a boolean to detect UA visual transitions on nav events.

This implements whatwg/html#8782.

I2P: https://groups.google.com/a/chromium.org/g/blink-dev/c/UJMYZXoSQ4A/m/OkIvKVtlAAAJ

Change-Id: I171dff85faa86f47ee8678f412c8f13091b88214
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4750342
Commit-Queue: Vladimir Levin <vmpstr@chromium.org>
Auto-Submit: Khushal Sagar <khushalsagar@chromium.org>
Reviewed-by: Vladimir Levin <vmpstr@chromium.org>
Commit-Queue: Khushal Sagar <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1181120}

html/browsers/browsing-the-web/history-traversal/popstate_event.html

@@ -21,6 +21,7 @@
     assert_true(e instanceof PopStateEvent, "is PopStateEvent");
     assert_false(e.bubbles, "bubbles");
     assert_false(e.cancelable, "cancelable");
+    assert_not_equals(e.hasUAVisualTransition, undefined);
 
     states.push(e.state);
 

navigation-api/navigate-event/navigate-navigation-back-same-document.html

@@ -23,6 +23,7 @@
         assert_equals(e.destination.index, 0);
         assert_equals(e.formData, null);
         assert_equals(e.info, "hi");
+        assert_not_equals(e.hasUAVisualTransition, undefined);
       });
       assert_true(navigation.canGoBack);
       navigation.back({ info: "hi" });