code: private boolean isValidMsgName(Node nameNode) {
      if (nameNode.isName() || nameNode.isStringKey()) {
        return nameNode.getString().startsWith("MSG_");
      } else if (nameNode.isQualifiedName()) {
        return nameNode.getLastChild().getString().startsWith("MSG_");
      } else {
        return false;
      }
    }
docs: Returns whether of not the given name is valid target for the result of goog.getMsg