[Doc] Add tip about running gclient sync after git rebase-update

This CL modifies commit_checklist.md to add a reminder to run gclient
sync -D after calling git rebase-update. Doing this removes third-
party build errors when trying to re-build after a rebase. This CL
also adds a tip about reverting CLs.

Bug: None
Change-Id: Id6a8072620a1162fbcdbe76b7f365b938287a785
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2450698
Commit-Queue: Toby Huang <[email protected]>
Reviewed-by: Michael Giuffrida <[email protected]>
Auto-Submit: Toby Huang <[email protected]>
Cr-Commit-Position: refs/heads/master@{#814822}
1 file changed