Create review1 on repo1.
Create review1b on top of review1. Set the topic to "crossrepo/test":
  log: Setting -1
  qabot Code-review -1
  message: "This review depends on an unmerged commit."
Abandon review1b
Set to the topic of review1 to "crossrepo/test":
  message: "This review is a cross-repo refactoring. It will be merged when all dependant reviews are mergeable."
  logged: "Detected atomic review on change xxx."
Create review2 on repo2 with topic crossrepo/test:
  message: "This review is a cross-repo refactoring. It will be merged when all dependant reviews are mergeable."
  logged: "Detected atomic review on review xxx."
Make review2 submittable:
  logged: "Change %d is submittable. Will try to merge all related changes."
Approve review1 but make it not mergeable (merge an other review that conflicts), then comment on review2: 
  logged: "Change %d is submittable. Will try to merge all related changes."
  comment: "Some related reviews to this cross-repo refactoring are not mergeable yet."
Make review1 mergeable:
  log DEBUG: "Change %d is mergeable"
  merged: review1 and review2