According to the author of the book, this verse is about God choosing a special person named Jehu to be a king. It tells us that Jehu was taken to a quiet room to get ready for his important job.
2 Kings 9:2: And when thou comest thither, look out there Jehu the son of Jehoshaphat the son of Nimshi, and go in, and make him arise up from among his brethren, and carry him to an inner chamber; [inner...: Heb. chamber in a chamber]
While 2 Kings 9:2 involves an anointing that leads to violence and kingship through force, 1 Samuel 26:9 promotes non-violence with David refusing to harm Saul, respecting God's anointed.
1 Samuel 26:9: And David said to Abishai, Destroy him not: for who can stretch forth his hand against the LORD'S anointed, and be guiltless?