git-cl: Make 'failed to add as cc' message less scary
git-cl: Make 'failed to add as cc' message less scary

BUG=665263

Change-Id: If72f3e5369ea0df170916c353be5188167c7aecb
Reviewed-on: https://chromium-review.googlesource.com/454977
Reviewed-by: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@chromium.org>
Commit-Queue: Aaron Gable <bbed39beedae4cdb499af742d2fcd6c63934d93b@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools