There's no need to put the error variables in a larger scope, nor define
them earlier than necessary. If anything, it makes the code harder to
follow, such as figuring out when nil errors are returned.
1. Changes travis configuration to use the chrome addon
2. Adds more command line options to runner package
3. Removes grab-headless_shell.sh script
4. Cleans up and adds some environment variables for controlling how
unit tests are ran
5. Fixes a minor issue in chromedp-gen on comment output (for working
with latest protocol definition)
