Add a rudimentary unit test for BandwidthController.

Bug: 26685616
Bug: 27506285
Change-Id: I4457abd43697a0425f167b81c1432d743800abb8
diff --git a/server/BandwidthController.h b/server/BandwidthController.h
index 3975303..f62cb1b 100644
--- a/server/BandwidthController.h
+++ b/server/BandwidthController.h
@@ -197,6 +197,10 @@
 
     std::list<QuotaInfo> quotaIfaces;
 
+    // For testing.
+    friend class BandwidthControllerTest;
+    static int (*execFunction)(int, char **, int *, bool, bool);
+    static FILE *(*popenFunction)(const char *, const char *);
 };
 
 #endif