Add visualization for Chrome configuration changes (fixes #3892)

- Add new API to retrieve/observe configuration values.
- cefclient: Add https://tests/config to inspect configuration
  values in real time.

tests/cefclient/browser/config_test.h

@@ -0,0 +1,18 @@
+// Copyright (c) 2025 The Chromium Embedded Framework Authors. All rights
+// reserved. Use of this source code is governed by a BSD-style license that
+// can be found in the LICENSE file.
+
+#ifndef CEF_TESTS_CEFCLIENT_BROWSER_CONFIG_TEST_H_
+#define CEF_TESTS_CEFCLIENT_BROWSER_CONFIG_TEST_H_
+#pragma once
+
+#include "tests/cefclient/browser/test_runner.h"
+
+namespace client::config_test {
+
+// Create message handlers. Called from test_runner.cc.
+void CreateMessageHandlers(test_runner::MessageHandlerSet& handlers);
+
+}  // namespace client::config_test
+
+#endif  // CEF_TESTS_CEFCLIENT_BROWSER_CONFIG_TEST_H_