[Blimp Net] Add EngineAuthHandler.

blimp/net/connection_handler.h

Index: blimp/net/connection_handler.h
diff --git a/blimp/net/connection_handler.h b/blimp/net/connection_handler.h
index b9d37f6199163030cd2fff0de551bda0a49eab72..afce887942c8af0f12ad45db3b71ccf3d5bdfe05 100644
--- a/blimp/net/connection_handler.h
+++ b/blimp/net/connection_handler.h
@@ -14,6 +14,9 @@ class ConnectionHandler {
  public:
   virtual ~ConnectionHandler() {}
 
+  // The receiving object is responsible for synchronously attaching its
+  // necessary delegates and observers to |connection| during the call to
+  // HandleConnection.
   virtual void HandleConnection(scoped_ptr<BlimpConnection> connection) = 0;
 };