Extract client handing from ChildMemoryCoordinatorImpl

components/memory_coordinator/common/client_registry.cc

+// Copyright 2016 The Chromium 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 "components/memory_coordinator/common/client_registry.h"
+
+namespace memory_coordinator {
+
+ClientRegistry::ClientRegistry() : clients_(new ClientList) {}
+
+ClientRegistry::~ClientRegistry() {}
+
+void ClientRegistry::RegisterClient(MemoryCoordinatorClient* client) {
+  clients_->AddObserver(client);
+}
+
+void ClientRegistry::UnregisterClient(MemoryCoordinatorClient* client) {
+  clients_->RemoveObserver(client);
+}
+
+}  // namespace memory_coordinator