title: Git: Authoring a commit that depends on multiple other Gerrit changes?
body: <p>At my place of work, we use a Gerrit server for code review.  Often times different people will author commits that are unrelated.  I've run into an issue where I must author a commit which depends on two other, unrelated commits.</p>
  
  <p>Let's say there are two commits on a gerrit server:</p>
  
  <ul>
  <li>Commit A: "Added function flipImage"</li>
  <li>Commit B: "Added function rotateImage"</li>
  </ul>
  
  <p>These two are independent of each other.  My job is to implement Commit C: "Added function flipRotateImage".  This requires both commits A and B to be present.</p>
  
  <p>I have two questions:</p>
  
  <ol>
  <li>How to I 'pull in' both A and B, and then author C, in such a way
  that I'm not actually changing A or B?  In other words I can't
  cherry-pick A or B because it would change them.  My goal is to be
  able to upload C for review without needing to update A &amp; B.</li>
  <li>Let's
  say the author of A uploads a new patch set.  I want to update my
  working branch such that the "A" in my chain is the latest "A", not
  an older patchset.  Can this be done?</li>
  </ol>