Support registration of custom preferences.

Custom global and request context preferences can now be registered via
CefBrowserProcessHandler::OnRegisterCustomPreferences. CefRequestContext
now extends CefPreferenceManager and global preferences can be accessed
via CefPreferenceManager::GetGlobalPreferenceManager.

libcef/browser/prefs/pref_registrar.cc

@@ -0,0 +1,99 @@
+// Copyright (c) 2022 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 "libcef/browser/prefs/pref_registrar.h"
+
+#include "include/cef_app.h"
+#include "include/cef_browser_process_handler.h"
+#include "include/cef_preference.h"
+#include "libcef/common/app_manager.h"
+#include "libcef/common/values_impl.h"
+
+#include "components/prefs/pref_registry_simple.h"
+#include "components/prefs/pref_store.h"
+
+namespace pref_registrar {
+
+namespace {
+
+class CefPreferenceRegistrarImpl : public CefPreferenceRegistrar {
+ public:
+  explicit CefPreferenceRegistrarImpl(PrefRegistrySimple* registry)
+      : registry_(registry) {}
+
+  CefPreferenceRegistrarImpl(const CefPreferenceRegistrarImpl&) = delete;
+  CefPreferenceRegistrarImpl& operator=(const CefPreferenceRegistrarImpl&) =
+      delete;
+
+  // CefPreferenceRegistrar methods.
+  bool AddPreference(const CefString& name,
+                     CefRefPtr<CefValue> default_value) override {
+    const std::string nameStr = name;
+    if (registry_->defaults()->GetValue(nameStr, nullptr)) {
+      LOG(ERROR) << "Trying to register a previously registered preference: "
+                 << nameStr;
+      return false;
+    }
+
+    switch (default_value->GetType()) {
+      case VTYPE_INVALID:
+      case VTYPE_NULL:
+      case VTYPE_BINARY:
+        break;
+      case VTYPE_BOOL:
+        registry_->RegisterBooleanPref(nameStr, default_value->GetBool());
+        return true;
+      case VTYPE_INT:
+        registry_->RegisterIntegerPref(nameStr, default_value->GetInt());
+        return true;
+      case VTYPE_DOUBLE:
+        registry_->RegisterDoublePref(nameStr, default_value->GetDouble());
+        return true;
+      case VTYPE_STRING:
+        registry_->RegisterStringPref(nameStr, default_value->GetString());
+        return true;
+      case VTYPE_DICTIONARY:
+      case VTYPE_LIST:
+        RegisterComplexPref(nameStr, default_value);
+        return true;
+    };
+
+    LOG(ERROR) << "Invalid value type for preference: " << nameStr;
+    return false;
+  }
+
+ private:
+  void RegisterComplexPref(const std::string& name,
+                           CefRefPtr<CefValue> default_value) {
+    CefValueImpl* impl = static_cast<CefValueImpl*>(default_value.get());
+
+    CefValueImpl::ScopedLockedValue scoped_locked_value(impl);
+    base::Value* impl_value = impl->GetValueUnsafe();
+
+    // Will make a deep copy of |impl_value|.
+    if (impl_value->type() == base::Value::Type::DICT) {
+      registry_->RegisterDictionaryPref(name, impl_value->Clone());
+    } else if (impl_value->type() == base::Value::Type::LIST) {
+      registry_->RegisterListPref(name, impl_value->Clone());
+    } else {
+      NOTREACHED();
+    }
+  }
+
+  PrefRegistrySimple* const registry_;
+};
+
+}  // namespace
+
+void RegisterCustomPrefs(cef_preferences_type_t type,
+                         PrefRegistrySimple* registry) {
+  if (auto app = CefAppManager::Get()->GetApplication()) {
+    if (auto handler = app->GetBrowserProcessHandler()) {
+      CefPreferenceRegistrarImpl registrar(registry);
+      handler->OnRegisterCustomPreferences(type, &registrar);
+    }
+  }
+}
+
+}  // namespace pref_registrar