chore: add assert lib

Author: sayjeyhi

message.js

@@ -40,6 +40,7 @@ goog.provide('jspb.ExtensionFieldInfo');
 goog.provide('jspb.Message');
 
 goog.require('goog.array');
+goog.require('goog.asserts');
 goog.require('goog.crypt.base64');
 goog.require('jspb.BinaryReader');
 goog.require('jspb.Map');