Move memory_coordinator_client and its registry to base/memory

base/memory/memory_coordinator_client.h

+// 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 BASE_MEMORY_MEMORY_COORDINATOR_CLIENT_H_
+#define BASE_MEMORY_MEMORY_COORDINATOR_CLIENT_H_
+
+#include "base/base_export.h"
+
+namespace base {
+
+enum class MemoryState {
+  UNKNOWN = -1,
+  NORMAL = 0,
+  THROTTLED = 1,
+  SUSPENDED = 2,
+};
+
+// This is an interface for components which can respond to memory status
+// changes.
+class BASE_EXPORT MemoryCoordinatorClient {
+ public:
+  virtual ~MemoryCoordinatorClient() {}
+
+  // Called when memory state has changed.
+  virtual void OnMemoryStateChange(MemoryState state) = 0;
+};
+
+}  // namespace base
+
+#endif  // BASE_MEMORY_MEMORY_COORDINATOR_CLIENT_H_