Extract client handing from ChildMemoryCoordinatorImpl

components/memory_coordinator/common/client_registry.cc

Index: components/memory_coordinator/common/client_registry.cc
diff --git a/components/memory_coordinator/common/client_registry.cc b/components/memory_coordinator/common/client_registry.cc
new file mode 100644
index 0000000000000000000000000000000000000000..57866c880d774fbfccf2638c484d3d64e3209989
--- /dev/null
+++ b/components/memory_coordinator/common/client_registry.cc
@@ -0,0 +1,21 @@
+// 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