Sundry tweaks to aos/vision libs

Change-Id: Ia5578dcf2d42ac53b81af239bf329eb084fcf1d9
diff --git a/aos/vision/events/tcp_client.h b/aos/vision/events/tcp_client.h
index 7ce01f7..74f1418 100644
--- a/aos/vision/events/tcp_client.h
+++ b/aos/vision/events/tcp_client.h
@@ -4,6 +4,7 @@
 #include "aos/vision/events/epoll_events.h"
 
 #include <memory>
+#include <string>
 
 namespace aos {
 namespace events {
@@ -11,7 +12,7 @@
 // Handles the client connection logic to hostname:portno
 class TcpClient : public EpollEvent {
  public:
-  TcpClient(const char *hostname, int portno);
+  TcpClient(const std::string &hostname, int portno);
 
   // Implement ReadEvent from EpollEvent to use this class.
 };