Use Chromium BUILD to approximate Blimp protocol version, and check it.

blimp/net/connection_error_observer.h

Index: blimp/net/connection_error_observer.h
diff --git a/blimp/net/connection_error_observer.h b/blimp/net/connection_error_observer.h
index da17db6f168e66776f899bd1024f658fe6c45f99..b00ea7886d44a425c121d0e5ba7d494c160bf0b3 100644
--- a/blimp/net/connection_error_observer.h
+++ b/blimp/net/connection_error_observer.h
@@ -12,6 +12,9 @@ class ConnectionErrorObserver {
   virtual ~ConnectionErrorObserver() {}
 
   // Called when a blimp connection encounters an error.
+  // Negative |error| values correspond directly to net/ error codes.
+  // Positive values indicate the EndConnection.reason code specified
+  // by the peer during a "clean" disconnection.
   virtual void OnConnectionError(int error) = 0;
 };