Fix a potential multi-thread issue when manipulating removable storage map

base/system_monitor/system_monitor.h

 // Copyright (c) 2012 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_SYSTEM_MONITOR_SYSTEM_MONITOR_H_
 #define BASE_SYSTEM_MONITOR_SYSTEM_MONITOR_H_
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/file_path.h"
 #include "base/string16.h"
+#include "base/synchronization/lock.h"
 #include "build/build_config.h"
 
 // Windows HiRes timers drain the battery faster so we need to know the battery
 // status.  This isn't true for other platforms.
 #if defined(OS_WIN)
 #define ENABLE_BATTERY_MONITORING 1
 #else
 #undef ENABLE_BATTERY_MONITORING
 #endif  // !OS_WIN
 
@@ skipping 71 matching lines @@
   // Returns information for attached removable storage.
   std::vector<RemovableStorageInfo> GetAttachedRemovableStorage() const;
 
   //
   // Power-related APIs
   //
 
   // Is the computer currently on battery power.
   // Can be called on any thread.
   bool BatteryPower() const {
     // Using a lock here is not necessary for just a bool.

[Philippe, 2012/12/14 13:53:03]

This is wrong on ARM multi cores.

[vandebo (ex-Chrome), 2013/01/04 19:46:54]

Feel free to fix.

     return battery_in_use_;
   }
 
   // Callbacks will be called on the thread which creates the SystemMonitor.
   // During the callback, Add/RemoveObserver will block until the callbacks
   // are finished. Observers should implement quick callback functions; if
   // lengthy operations are needed, the observer should take care to invoke
   // the operation on an appropriate thread.
   class BASE_EXPORT PowerObserver {
    public:
@@ skipping 94 matching lines @@
 
 #if defined(ENABLE_BATTERY_MONITORING)
   base::OneShotTimer<SystemMonitor> delayed_battery_check_;
 #endif
 
 #if defined(OS_IOS)
   // Holds pointers to system event notification observers.
   std::vector<id> notification_observers_;
 #endif
 
+  // For manipulating removable_storage_map_ structure.
+  mutable base::Lock removable_storage_lock_;
   // Map of all the attached removable storage devices.
   RemovableStorageMap removable_storage_map_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemMonitor);
 };
 
 }  // namespace base
 
 #endif  // BASE_SYSTEM_MONITOR_SYSTEM_MONITOR_H_