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.

libcef/browser/setting_helper.cc

@@ -0,0 +1,118 @@
+// 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.
+
+#include "cef/libcef/browser/setting_helper.h"
+
+#include "cef/include/cef_request_context.h"
+#include "cef/libcef/browser/thread_util.h"
+#include "components/content_settings/core/browser/host_content_settings_map.h"
+#include "url/gurl.h"
+
+namespace setting_helper {
+
+class RegistrationImpl final : public Registration, public CefRegistration {
+ public:
+  RegistrationImpl(Registrar* registrar, CefRefPtr<CefSettingObserver> observer)
+      : registrar_(registrar), observer_(observer) {
+    DCHECK(registrar_);
+    DCHECK(observer_);
+  }
+
+  RegistrationImpl(const RegistrationImpl&) = delete;
+  RegistrationImpl& operator=(const RegistrationImpl&) = delete;
+
+  ~RegistrationImpl() override {
+    CEF_REQUIRE_UIT();
+    if (registrar_) {
+      registrar_->RemoveObserver(this);
+    }
+  }
+
+  void Detach() override {
+    registrar_ = nullptr;
+    observer_ = nullptr;
+  }
+
+  void RunCallback(const CefString& requesting_url,
+                   const CefString& top_level_url,
+                   cef_content_setting_types_t content_type) const override {
+    observer_->OnSettingChanged(requesting_url, top_level_url, content_type);
+  }
+
+ private:
+  raw_ptr<Registrar> registrar_;
+  CefRefPtr<CefSettingObserver> observer_;
+
+  IMPLEMENT_REFCOUNTING_DELETE_ON_UIT(RegistrationImpl);
+};
+
+Registrar::~Registrar() {
+  RemoveAll();
+}
+
+void Registrar::Init(HostContentSettingsMap* settings) {
+  DCHECK(settings);
+  DCHECK(IsEmpty() || settings_ == settings);
+  settings_ = settings;
+}
+
+void Registrar::Reset() {
+  RemoveAll();
+  settings_ = nullptr;
+}
+
+void Registrar::RemoveAll() {
+  if (!observers_.empty()) {
+    settings_->RemoveObserver(this);
+    for (auto& registration : observers_) {
+      registration.Detach();
+    }
+    observers_.Clear();
+  }
+}
+
+bool Registrar::IsEmpty() const {
+  return observers_.empty();
+}
+
+CefRefPtr<CefRegistration> Registrar::AddObserver(
+    CefRefPtr<CefSettingObserver> observer) {
+  CHECK(settings_);
+
+  RegistrationImpl* impl = new RegistrationImpl(this, observer);
+
+  if (observers_.empty()) {
+    settings_->AddObserver(this);
+  }
+  observers_.AddObserver(impl);
+
+  return impl;
+}
+
+void Registrar::RemoveObserver(Registration* registration) {
+  CHECK(settings_);
+
+  observers_.RemoveObserver(registration);
+  if (observers_.empty()) {
+    settings_->RemoveObserver(this);
+  }
+}
+
+void Registrar::OnContentSettingChanged(
+    const ContentSettingsPattern& primary_pattern,
+    const ContentSettingsPattern& secondary_pattern,
+    ContentSettingsTypeSet content_type_set) {
+  DCHECK(!IsEmpty());
+
+  const CefString requesting_url(primary_pattern.ToRepresentativeUrl().spec());
+  const CefString top_level_url(secondary_pattern.ToRepresentativeUrl().spec());
+  const auto content_type =
+      static_cast<cef_content_setting_types_t>(content_type_set.GetType());
+
+  for (Registration& registration : observers_) {
+    registration.RunCallback(requesting_url, top_level_url, content_type);
+  }
+}
+
+}  // namespace setting_helper