patch from issue 290683003
Separate processing from fetching
Re-write to walk release branches instead of trunk
Print skipped counts, recover from json errors, always fetch history json
Don't show missing review warning for bot authors
Limit by branches instead of commits, and various refactorings
Generalize to support blink
Add graph command, remove milliseconds, keep per-branch files
Fix timezone of commit times
Attempt to break down time further
Make it possible to run the script outside of a chrome checkout