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

blimp/client/session/assignment_source.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "blimp/client/session/assignment_source.h"
 
 #include "base/bind.h"
 #include "base/callback_helpers.h"
 #include "base/command_line.h"
 #include "base/files/file_util.h"
@@ skipping 225 matching lines @@
   url_fetcher_ =
       net::URLFetcher::Create(assigner_endpoint_, net::URLFetcher::POST, this);
   url_fetcher_->SetRequestContext(url_request_context_.get());
   url_fetcher_->SetLoadFlags(net::LOAD_DO_NOT_SAVE_COOKIES |
                              net::LOAD_DO_NOT_SEND_COOKIES);
   url_fetcher_->AddExtraRequestHeader("Authorization: Bearer " +
                                       client_auth_token);
 
   // Write the JSON for the request data.
   base::DictionaryValue dictionary;
-  dictionary.SetString(kProtocolVersionKey, blimp::kEngineVersion);
+  dictionary.SetString(kProtocolVersionKey,
+                       base::IntToString(kProtocolVersion));
   std::string json;
   base::JSONWriter::Write(dictionary, &json);
   url_fetcher_->SetUploadData("application/json", json);
   url_fetcher_->Start();
 }
 
 void AssignmentSource::OnURLFetchComplete(const net::URLFetcher* source) {
   DCHECK(!callback_.is_null());
   DCHECK_EQ(url_fetcher_.get(), source);
 
@@ skipping 114 matching lines @@
 }
 
 void AssignmentSource::OnJsonParseError(const std::string& error) {
   DLOG(ERROR) << "Error while parsing assigner JSON: " << error;
   base::ResetAndReturn(&callback_)
       .Run(AssignmentSource::Result::RESULT_BAD_RESPONSE, Assignment());
 }
 
 }  // namespace client
 }  // namespace blimp