Added memory-monitor for ChromeOS.

content/browser/memory/memory_monitor_linux.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 CONTENT_BROWSER_MEMORY_MEMORY_MONITOR_LINUX_H_
 #define CONTENT_BROWSER_MEMORY_MEMORY_MONITOR_LINUX_H_
 
 #include "content/browser/memory/memory_monitor.h"
 #include "content/common/content_export.h"
 
-namespace base {
-struct SystemMemoryInfoKB;
-}  // namespace base
-
 namespace content {
 
 // A memory monitor for the Linux platform.
 class CONTENT_EXPORT MemoryMonitorLinux : public MemoryMonitor {
  public:
   MemoryMonitorLinux(MemoryMonitorDelegate* delegate);
   ~MemoryMonitorLinux() override;
 
   // MemoryMonitor:
   int GetFreeMemoryUntilCriticalMB() override;
 
   // Factory function to create an instance of this class.
   static std::unique_ptr<MemoryMonitorLinux> Create(
       MemoryMonitorDelegate* delegate);
 
  private:
   // The delegate to be used for retrieving system memory information. Used as a
   // testing seam.
   MemoryMonitorDelegate* delegate_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_MEMORY_MEMORY_MONITOR_LINUX_H_