adb: allow use of arbitrary socket specs for command socket.

Bug: http://b/30445394
Change-Id: I474ede35ec3c56ad86da503c9703f83ef5e80862
diff --git a/adb/socket_spec.h b/adb/socket_spec.h
index 69efb07..6302da5 100644
--- a/adb/socket_spec.h
+++ b/adb/socket_spec.h
@@ -20,6 +20,7 @@
 
 // Returns true if the argument starts with a plausible socket prefix.
 bool is_socket_spec(const std::string& spec);
+bool is_local_socket_spec(const std::string& spec);
 
 int socket_spec_connect(const std::string& spec, std::string* error);
 int socket_spec_listen(const std::string& spec, std::string* error,