First, we want all of the functionality in a single package; this means
collapsing whatever is useful into the root chromedp package.
The runner package is being replaced by the Allocator interface, with a
default implementation which starts browser processes.
The client package doesn't really have a place in the new design. The
context, allocator, and browser types will handle the connection with
each browser.
Finally, the new API is context-based, hence the addition of context.go.
The tests have been modified to build and run against the new API.
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)
