Extract client handing from ChildMemoryCoordinatorImpl

components/memory_coordinator/common/client_registry.h

Index: components/memory_coordinator/common/client_registry.h
diff --git a/components/memory_coordinator/common/client_registry.h b/components/memory_coordinator/common/client_registry.h
new file mode 100644
index 0000000000000000000000000000000000000000..593b9fa8faab816dfdc594c58b167e4b4089c2ae
--- /dev/null
+++ b/components/memory_coordinator/common/client_registry.h
@@ -0,0 +1,34 @@
+// 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.
+
+#ifndef COMPONENTS_MEMORY_COORDINATOR_COMMON_CLIENT_REGISTRY_H_
+#define COMPONENTS_MEMORY_COORDINATOR_COMMON_CLIENT_REGISTRY_H_
+
+#include "base/observer_list_threadsafe.h"
+#include "components/memory_coordinator/common/memory_coordinator_client.h"
+
+namespace memory_coordinator {
+
+// ClientRegistry is a base class of process-specific memory coordinator
+// and provides ways to register/unregister MemoryCoordinatorClients.
+class ClientRegistry {
+ public:
+  ClientRegistry();
+  virtual ~ClientRegistry();
+
+  // Registers/unregisters a client. Does not take ownership of client.
+  void RegisterClient(MemoryCoordinatorClient* client);
+  void UnregisterClient(MemoryCoordinatorClient* client);
+
+ protected:
+  using ClientList = base::ObserverListThreadSafe<MemoryCoordinatorClient>;
+  ClientList* clients() { return clients_.get(); }
+
+ private:
+  scoped_refptr<ClientList> clients_;
+};
+
+}  // namespace memory_coordinator
+
+#endif  // COMPONENTS_MEMORY_COORDINATOR_COMMON_CLIENT_REGISTRY_H_