Reduce header dependencies in base/

base/system_monitor.h

 // Copyright (c) 2008 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_H_
 #define BASE_SYSTEM_MONITOR_H_
 
-#include "base/observer_list_threadsafe.h"
-#include "base/singleton.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
 
+#include "base/observer_list_threadsafe.h"
+#include "base/singleton.h"
+#if defined(ENABLE_BATTERY_MONITORING)
+#include "base/timer.h"
+#endif  // defined(ENABLE_BATTERY_MONITORING)
+
 namespace base {
 
 // Class for monitoring various system-related subsystems
 // such as power management, network status, etc.
 // TODO(mbelshe):  Add support beyond just power management.
 class SystemMonitor {
  public:
   // Access to the Singleton
   static SystemMonitor* Get() {

[M-A Ruel, 2009/06/03 14:28:37]

Humm I'd rather have this function implementation in system_monitor.cc. This
way, you can also remove singleton.h.

     // Uses the LeakySingletonTrait because cleanup is optional.
     return
         Singleton<SystemMonitor, LeakySingletonTraits<SystemMonitor> >::get();
   }
 
   // Start the System Monitor within a process.  This method
   // is provided so that the battery check can be deferred.
   // The MessageLoop must be started before calling this
   // method.
   // This is a no-op on platforms for which ENABLE_BATTERY_MONITORING is
@@ skipping 82 matching lines @@
 #if defined(ENABLE_BATTERY_MONITORING)
   base::OneShotTimer<SystemMonitor> delayed_battery_check_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(SystemMonitor);
 };
 
 }
 
 #endif  // BASE_SYSTEM_MONITOR_H_