Adds an iOS implementation of base::SystemMonitor.

base/system_monitor/system_monitor.h

Index: base/system_monitor/system_monitor.h
diff --git a/base/system_monitor/system_monitor.h b/base/system_monitor/system_monitor.h
index d960fa2d24e735df4e3f8f04775233e6c0575d4a..fe91c4946afb83b8dc1a92c06bceb4484a16824f 100644
--- a/base/system_monitor/system_monitor.h
+++ b/base/system_monitor/system_monitor.h
@@ -27,10 +27,14 @@
 #include "base/timer.h"
 #endif  // defined(ENABLE_BATTERY_MONITORING)
 
-#if defined(OS_MACOSX)
+#if defined(OS_MACOSX) && !defined(OS_IOS)
 #include <IOKit/pwr_mgt/IOPMLib.h>
 #include <IOKit/IOMessage.h>
-#endif  // OS_MACOSX
+#endif  // OS_MACOSX && !OS_IOS
+
+#if defined(OS_IOS)
+#include <objc/runtime.h>  // For id.
+#endif  // OS_IOS
 
 class FilePath;
 
@@ -189,6 +193,11 @@ class BASE_EXPORT SystemMonitor {
   base::OneShotTimer<SystemMonitor> delayed_battery_check_;
 #endif
 
+#if defined(OS_IOS)
+  // Holds pointers to system event notification observers.
+  std::vector<id> notification_observers_;
+#endif
+
   MediaDeviceMap media_device_map_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemMonitor);