[automerger skipped] Support booting a chained boot-debug.img
am: 9d7d26a5cf -s ours
am skip reason: change_id Idfa8caffbb96f33702b1749afd2e2a59616ddba7 with SHA1 705fd7f52c is in history

Change-Id: Ie9fb187c71c0233fb6e8ac75676aa8f5226f0fc7