update_engine: Update libchrome APIs to r369476

The new libchrome has been ported from Chromium and some APIs have
changed. Make necessary changes at call sites.

Change-Id: I42e65bda7f1dbdf6f6e0ebf356d2cfea6b729193
diff --git a/update_attempter.cc b/update_attempter.cc
index da135e4..9b68c44 100644
--- a/update_attempter.cc
+++ b/update_attempter.cc
@@ -851,7 +851,7 @@
   command.push_back("/sbin/shutdown");
   command.push_back("-r");
   command.push_back("now");
-  LOG(INFO) << "Running \"" << JoinString(command, ' ') << "\"";
+  LOG(INFO) << "Running \"" << base::JoinString(command, " ") << "\"";
   int rc = 0;
   Subprocess::SynchronousExec(command, &rc, nullptr);
   return rc == 0;