Make auto-roll script work with separate Chromium checkouts.

* Add optional --chromium-checkout flag to point out the Chromium checkout to
work in (automatic fallback to current working dir if that's a Chromium checkout).
* Introduce logging and --verbose flag.
* Make functions private and adopt Python style guide.
* Made --dry-run perform the presubmit checks and other stuff for --commit, except the actual commit.
* Add EDITOR=true environment to 'git cl upload' to avoid launching an interactive editor.
* Removed interactive invocation of 'git cl upload' and 'git cl land'

BUG=chromium:433305
TESTED=Muliple local runs using:
tools/autoroller/roll_webrtc_in_chromium.py --chromium-checkout /path/to/chrome/src --dry-run --verbose
tools/autoroller/roll_webrtc_in_chromium.py --chromium-checkout /path/to/chrome/src --dry-run --abort
tools/autoroller/roll_webrtc_in_chromium.py --chromium-checkout /path/to/chrome/src --dry-run --status
cd /path/to/chrome/src
/path/to/webrtc/src/tools/autoroller/roll_webrtc_in_chromium.py --dry-run --verbose

R=phoglund@webrtc.org, tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/46559004

Cr-Commit-Position: refs/heads/master@{#8694}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8694 4adac7df-926f-26a2-2b94-8c16560cd09d
1 file changed