Instead we use the packages directory which is at the same
level as the BUILD.gn file. That's a bit of a broken assumption
but it happens to work for all our skyx uses for now.
@abarth
This patch contains some minor improvements to the network service:
- We now cache the connection to the network service so we don't need to spin
it up for each request.
- We now manage the lifetime of NetworkServiceImpl in the same way as other
services.
Also, update the workbench sky_tools dependency to the latest version.
The workbench package exists to pull in pub packages from both pub.dartlang.org
and from the source tree (using dependency overrides). The idea is that
workbench will reflect a typical Sky developer's environment so that we can use
the same tools as a typical sky developer by running them with the workbench as
the cwd.
