Use same warn_common.py and warn.py for Android and Chrome

* add chrome_project_list.py
* use newer Chrome's warn_common.py and severity.py
* modify warn_common.py to work with both python2 and python3,
  to work with and without google3

Test: warn.py --url=http://cs/android --separator='?l=' build.log > warnings.html
Test: warn.py --gencsv build.log > warnings.csv
Change-Id: I9aeee7031c11988d8ead1733ff4846ae6cb1ee73