I needed to merge a CL into a branch, and do manual changes to it. I followed the process at http://commondatastorage.googleapis.com/chrome-infra-docs/flat/depot_tools/docs/html/git-drover.html but I used "git cl upload -gerrit" instead of "git cl upload".

Initially, "git cl upload --gerrit" failed to upload the CL with the following output:

remote: Processing changes: refs: 1, done            
remote: (W) 6c05b2b: commit subject >50 characters; use shorter first paragraph        
To https://chromium.googlesource.com/a/chromium/src.git
 ! [remote rejected]           6c05b2b98c7e3adfc99cd5ad0a8623346ba07a53 -> refs/for/refs/branch-heads/3112%m=Initial_upload,notify=NONE (change https://chromium-review.googlesource.com/540103 closed)
error: failed to push some refs to 'https://chromium.googlesource.com/a/chromium/src.git'

Error after CL description prompt -- saving description to /usr/local/google/home/costan/.git_cl_description_backup

Failed to create a change. Please examine output above for the reason of the failure.
Hint: run command below to diagnose common Git/Gerrit credential problems:
  git cl creds-check


Per help from agable@, I worked around this problem by removing the Change-Id: header from the commit message. However, the manually merged CL does not point to the original CL, like git-drover's merged CL.

Original CL: http://crrev.com/c/538965
Merged by git-drover: http://crrev.com/c/540103
Manual merge (with changes): http://crrev.com/c/541797

I can prepare a CL that documents the Change-Id: workaround. However, I don't know what's the right thing to do about the 2nd issue.