feat(extension): expose host version and WebView page events

ui/flutter/lib/app/rpc/webview_event_script.dart

@@ -0,0 +1,40 @@
+import 'dart:convert';
+
+/// Runs before page scripts and reports only the main document's events.
+String buildWebViewEventScript(String channel) =>
+    '''
+(() => {
+  if (window !== window.top) return;
+  const pending = [];
+  const flush = () => {
+    const bridge = window.flutter_inappwebview;
+    if (!bridge || typeof bridge.callHandler !== 'function') return;
+    while (pending.length) bridge.callHandler(${jsonEncode(channel)}, JSON.stringify(pending.shift()));
+  };
+  const send = (event, data) => { pending.push({event, data}); flush(); };
+  window.addEventListener('flutterInAppWebViewPlatformReady', flush);
+  let lastURL = String(location.href);
+  const changed = () => {
+    const url = String(location.href);
+    if (url === lastURL) return;
+    lastURL = url;
+    send('url-changed', {url, sameDocument: true});
+  };
+  send('url-changed', {url: lastURL, sameDocument: false});
+  for (const name of ['pushState', 'replaceState']) {
+    const original = history[name];
+    history[name] = function(...args) {
+      const result = Reflect.apply(original, this, args);
+      changed();
+      return result;
+    };
+  }
+  window.addEventListener('hashchange', changed);
+  window.addEventListener('popstate', changed);
+  window.addEventListener('pageshow', (event) => {
+    if (event.persisted) send('url-changed', {url: String(location.href), sameDocument: false});
+    else changed();
+  });
+  window.addEventListener('load', () => send('load', {url: String(location.href)}), {once: true});
+})();
+''';