Linux SxS: Use a non-colliding path for Debian packages.

This also adds compatibility symlinks so that running browsers continue
to work (as a workaround for not everything going through the zygote).

Next steps: same change for RPM, remove remaining collisions outside of /opt.

BUG=38598
R=thestig@chromium.org

Review URL: https://codereview.chromium.org/81933002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236814 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236814