Handle pairing_client_id in the negotiating authenticators.

remoting/protocol/negotiating_authenticator_base.h

Index: remoting/protocol/negotiating_authenticator_base.h
diff --git a/remoting/protocol/negotiating_authenticator_base.h b/remoting/protocol/negotiating_authenticator_base.h
index 243359fd706ca05a67d8476063c975db40d865b6..9e5576ade77b5604d52fd1d42febdbe36852dc62 100644
--- a/remoting/protocol/negotiating_authenticator_base.h
+++ b/remoting/protocol/negotiating_authenticator_base.h
@@ -109,6 +109,9 @@ class NegotiatingAuthenticatorBase : public Authenticator {
   static const buzz::StaticQName kSupportedMethodsAttributeQName;
   static const char kSupportedMethodsSeparator;
 
+  static const buzz::StaticQName kPairingInfoTag;
+  static const buzz::StaticQName kClientIdAttribute;
+
   // Parses a string that defines an authentication method. Returns
   // Method::INVALID if the string is invalid.
   static Method ParseMethodString(const std::string& value);