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

blimp/common/create_blimp_message.cc

Index: blimp/common/create_blimp_message.cc
diff --git a/blimp/common/create_blimp_message.cc b/blimp/common/create_blimp_message.cc
index 43d4377803623c65b5afcbb09a33391869ff370b..5b69013b03ade40862727074519cc16e104f548a 100644
--- a/blimp/common/create_blimp_message.cc
+++ b/blimp/common/create_blimp_message.cc
@@ -126,4 +126,19 @@ std::unique_ptr<BlimpMessage> CreateCheckpointAckMessage(
   return output;
 }
 
+std::unique_ptr<BlimpMessage> CreateEndConnectionMessage(
+    EndConnectionMessage::Reason reason) {
+  std::unique_ptr<BlimpMessage> output(new BlimpMessage);
+  output->set_type(BlimpMessage::PROTOCOL_CONTROL);
+
+  ProtocolControlMessage* control_message = output->mutable_protocol_control();
+  control_message->set_type(ProtocolControlMessage::END_CONNECTION);
+
+  EndConnectionMessage* end_connection_message =
+      control_message->mutable_end_connection();
+  end_connection_message->set_reason(reason);
+
+  return output;
+}
+
 }  // namespace blimp