Avoid redundant image requests.
Avoid redundant image requests.

When rendering services, avoid redundant image requests due to
setting href attributes on SVG elements to values they already
have.

R=benji, bac
CC=
https://codereview.appspot.com/9731048

mitechie/juju-gui,mitechie/juju-gui,bac/juju-gui,CanonicalJS/juju-gui,jrwren/juju-gui,bac/juju-gui,jrwren/juju-gui,mitechie/juju-gui,CanonicalJS/juju-gui,CanonicalJS/juju-gui,bac/juju-gui,mitechie/juju-gui,jrwren/juju-gui,jrwren/juju-gui,bac/juju-gui