Added MemoryMonitor for Linux (with test)

components/memory_coordinator/browser/memory_monitor.h

 // 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"
 #include "components/memory_coordinator/common/memory_coordinator_export.h"
 
+namespace base {
+struct SystemMemoryInfoKB;
+}
+
 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 MEMORY_COORDINATOR_EXPORT 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.
 MEMORY_COORDINATOR_EXPORT std::unique_ptr<MemoryMonitor> CreateMemoryMonitor();
 
+
+// A class for fetching system information used by a memory monitor. This can
+// be subclassed for testing or if a particular MemoryMonitor implementation
+// needs additional functionality.
+class MEMORY_COORDINATOR_EXPORT MemoryMonitorDelegate {
+ public:
+  MemoryMonitorDelegate() {}
+  virtual ~MemoryMonitorDelegate();
+
+  // Returns system memory information.
+  virtual void GetSystemMemoryInfo(base::SystemMemoryInfoKB* mem_info);
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MemoryMonitorDelegate);
+};
+
 }  // namespace memory_coordinator
 
 #endif  // COMPONENTS_MEMORY_COORDINATOR_BROWSER_MEMORY_MONITOR_H_