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

blimp/common/version_info.cc.version

Index: blimp/common/version_info.cc.version
diff --git a/blimp/common/version_info.cc.version b/blimp/common/version_info.cc.version
new file mode 100644
index 0000000000000000000000000000000000000000..76f1457cd7d614c521f0303e342ef5d0377a40d6
--- /dev/null
+++ b/blimp/common/version_info.cc.version
@@ -0,0 +1,18 @@
+// 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/common/version_info.h"
+
+namespace blimp {
+
+std::string GetAssignmentRequestVersion() {
+  // Assignment API currently only knows one version.
+  return "20160209094838";
+}
+
+int GetProtocolVersion() {
+  return @BUILD@;
+}
+
+}  // namespace blimp