Add missing includes.

Change-Id: Ib697ce44243e7cb07aee60944238e0854d82e9de
diff --git a/media/libcpustats/ThreadCpuUsage.cpp b/media/libcpustats/ThreadCpuUsage.cpp
index 7b5b661..b43b36c 100644
--- a/media/libcpustats/ThreadCpuUsage.cpp
+++ b/media/libcpustats/ThreadCpuUsage.cpp
@@ -19,6 +19,7 @@
 
 #include <errno.h>
 #include <stdlib.h>
+#include <string.h>
 #include <time.h>
 
 #include <utils/Log.h>