installd: add missing <functional> for std::function.

Bug: b/175635923
Test: treehugger
Change-Id: I2541263d27b5bced25667baaf814bff0e65e4604
diff --git a/cmds/installd/utils.h b/cmds/installd/utils.h
index ecea1d2..c43fdbd 100644
--- a/cmds/installd/utils.h
+++ b/cmds/installd/utils.h
@@ -18,6 +18,7 @@
 #ifndef UTILS_H_
 #define UTILS_H_
 
+#include <functional>
 #include <string>
 #include <vector>