Introduce MemoryCoordinatorProxy in base

base/memory/memory_coordinator_proxy.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 "base/memory/memory_coordinator_proxy.h"
+
+namespace base {
+
+MemoryCoordinatorProxy::MemoryCoordinatorProxy() {
+}
+
+MemoryCoordinatorProxy::~MemoryCoordinatorProxy() {
+}
+
+MemoryCoordinatorProxy* MemoryCoordinatorProxy::GetInstance() {
+  return Singleton<base::MemoryCoordinatorProxy>::get();
+}
+
+MemoryState MemoryCoordinatorProxy::GetCurrentMemoryState() const {
+  if (!callback_)
+    return MemoryState::NORMAL;
+  return callback_.Run();
+}
+
+void MemoryCoordinatorProxy::SetGetCurrentMemoryStateCallback(
+    GetCurrentMemoryStateCallback callback) {
+  callback_ = callback;
+}
+
+}  // namespace base