Create MemoryMonitor and Windows implementation.

components/memory_coordinator/browser/memory_monitor.h

Index: components/memory_coordinator/browser/memory_monitor.h
diff --git a/components/memory_coordinator/browser/memory_monitor.h b/components/memory_coordinator/browser/memory_monitor.h
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+++ b/components/memory_coordinator/browser/memory_monitor.h
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+// Copyright (c) 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_BROWSER_MEMORY_MONITOR_H_
+#define COMPONENTS_MEMORY_COORDINATOR_BROWSER_MEMORY_MONITOR_H_
+
+#include <memory>
+
+#include "base/macros.h"
+
+namespace memory_coordinator {
+
+// A simple class that monitors the amount of free memory available on a system.
+// This is an interface to facilitate dependency injection for testing.
+class MemoryMonitor {
+ public:
+  MemoryMonitor() {}
+  virtual ~MemoryMonitor() {}
+
+  // Returns the amount of free memory available on the system until the system
+  // will be in a critical state. Critical is as defined by the OS (swapping
+  // will occur, or physical memory will run out, etc). It is possible for this
+  // to return negative values, in which case that much memory would have to be
+  // freed in order to exit a critical memory state.
+  virtual int GetFreeMemoryUntilCriticalMB() = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MemoryMonitor);
+};
+
+// Factory function for creating a monitor for the current platform.
+std::unique_ptr<MemoryMonitor> CreateMemoryMonitor();
+
+}  // namespace memory_coordinator
+
+#endif  // COMPONENTS_MEMORY_COORDINATOR_BROWSER_MEMORY_MONITOR_H_