Add cdbs to install-build-deps
The Common Debian Build System (cdbs) is needed for
packaging .deb files in some configurations.
http://packages.ubuntu.com/search?keywords=cdbs
shows that it's available for all common Ubuntu
distributions.
On Precise and Trusty, the package is very small (~40kB),
so it shouldn't have much impact on users.
TESTED=ran install-build-deps.sh on Ubuntu Precise.
R=friedman@chromium.org
Review URL: https://codereview.chromium.org/
531513002
Cr-Commit-Position: refs/heads/master@{#295674}