shill: vpn: Add support for the OpenVPN.TLSAuthContents property.

BUG=chromium-os:28793
TEST=unit tests

Change-Id: Ib168fb506487e87a87fbb8c631d723b4f0241dc7
Reviewed-on: https://gerrit.chromium.org/gerrit/19452
Tested-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: Sam Leffler <sleffler@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Ready: Darin Petkov <petkov@chromium.org>
diff --git a/openvpn_driver.h b/openvpn_driver.h
index 1470454..74a156f 100644
--- a/openvpn_driver.h
+++ b/openvpn_driver.h
@@ -9,6 +9,7 @@
 #include <string>
 #include <vector>
 
+#include <base/file_path.h>
 #include <base/memory/scoped_ptr.h>
 #include <gtest/gtest_prod.h>  // for FRIEND_TEST
 
@@ -161,6 +162,7 @@
   scoped_ptr<RPCTask> rpc_task_;
   std::string tunnel_interface_;
   VPNRefPtr device_;
+  FilePath tls_auth_file_;
 
   // The PID of the spawned openvpn process. May be 0 if no process has been
   // spawned yet or the process has died.