Added missing header to window.h

Added string.h for memset()

Change-Id: I48ebec4df82bb9ae0b5daac3c653b9c4dc42c502
Signed-off-by: Homin Lee <suapapa@insignal.co.kr>

include/system/window.h

@@ -18,6 +18,7 @@
 #define SYSTEM_CORE_INCLUDE_ANDROID_WINDOW_H
 
 #include <stdint.h>
+#include <string.h>
 #include <sys/cdefs.h>
 #include <system/graphics.h>
 #include <cutils/native_handle.h>