Add missing includes.

Includes are transitively imported by <string> in String8.h + String16.h
but that include is being removed.

Test: pass
Change-Id: Ide5c011b40b4a4f031dd26ead08b5c8d5d299693
diff --git a/libutils/Printer.cpp b/libutils/Printer.cpp
index 9573a10..12f77bb 100644
--- a/libutils/Printer.cpp
+++ b/libutils/Printer.cpp
@@ -21,6 +21,8 @@
 #include <utils/String8.h>
 #include <utils/Log.h>
 
+#include <stdlib.h>
+
 namespace android {
 
 /*