Add read barriers for the GC roots in Instrumentation.

Bug: 12687968
Change-Id: I324e2f950ce4500b0e00722044af3a9c82487b23
diff --git a/runtime/runtime.h b/runtime/runtime.h
index 284e4ff..6a5fe75 100644
--- a/runtime/runtime.h
+++ b/runtime/runtime.h
@@ -21,6 +21,7 @@
 #include <stdio.h>
 
 #include <iosfwd>
+#include <set>
 #include <string>
 #include <utility>
 #include <vector>