Refactor of Authenticator to allow it to ProcessMessage asynchronously and then call a callback

remoting/protocol/negotiating_authenticator.cc

Index: remoting/protocol/negotiating_authenticator.cc
diff --git a/remoting/protocol/negotiating_authenticator.cc b/remoting/protocol/negotiating_authenticator.cc
index ad3ed4dc780295106f46d1dec14e89f00759f72f..30a11e1adad6f2ceee35ae814cb23f2aca4114d5 100644
--- a/remoting/protocol/negotiating_authenticator.cc
+++ b/remoting/protocol/negotiating_authenticator.cc
@@ -90,7 +90,9 @@ NegotiatingAuthenticator::rejection_reason() const {
   return rejection_reason_;
 }
 
-void NegotiatingAuthenticator::ProcessMessage(const buzz::XmlElement* message) {
+void NegotiatingAuthenticator::ProcessMessage(
+    const base::Closure& resume_callback,
+    const buzz::XmlElement* message) {
   DCHECK_EQ(state(), WAITING_MESSAGE);
 
   std::string method_attr = message->Attr(kMethodAttributeQName);
@@ -112,6 +114,7 @@ void NegotiatingAuthenticator::ProcessMessage(const buzz::XmlElement* message) {
       // Message contains neither method nor supported-methods attributes.
       state_ = REJECTED;
       rejection_reason_ = PROTOCOL_ERROR;
+      resume_callback.Run();
       return;
     }
 
@@ -136,6 +139,7 @@ void NegotiatingAuthenticator::ProcessMessage(const buzz::XmlElement* message) {
       // Failed to find a common auth method.
       state_ = REJECTED;
       rejection_reason_ = PROTOCOL_ERROR;
+      resume_callback.Run();
       return;
     }
 
@@ -153,13 +157,27 @@ void NegotiatingAuthenticator::ProcessMessage(const buzz::XmlElement* message) {
   }
 
   if (state_ == WAITING_MESSAGE) {
-    current_authenticator_->ProcessMessage(message);
-    state_ = current_authenticator_->state();
-    if (state_ == REJECTED)
-      rejection_reason_ = current_authenticator_->rejection_reason();
+    // |this| outlives current_authenticator_, so using Unretained is safe here.
+    current_authenticator_->ProcessMessage(
+        base::Bind(&NegotiatingAuthenticator::UpdateState,
+                   base::Unretained(this), resume_callback),
+        message);
+  } else {
+    UpdateState(resume_callback);
   }
 }
 
+void NegotiatingAuthenticator::UpdateState(
+    const base::Closure& resume_callback) {
+  // After the underlying authenticator finishes processing the message, the
+  // NegotiatingAuthenticator must update its own state before running the
+  // |resume_callback| to resume the session negotiation.
+  state_ = current_authenticator_->state();
+  if (state_ == REJECTED)
+    rejection_reason_ = current_authenticator_->rejection_reason();
+  resume_callback.Run();
+}
+
 scoped_ptr<buzz::XmlElement> NegotiatingAuthenticator::GetNextMessage() {
   DCHECK_EQ(state(), MESSAGE_READY);