Only use request.root if it exists

Fixes chrome extension build
Add extension build to Travis
Remove last traces of chameleon

The Chrome extension build still required chameleon, a dependency
removed by 81ce4b1.

This commit removes the last traces of chameleon (from the extension
builder and the views file) and thus fixes the Chrome build for new
checkouts.
Ensure extension build has `request.root`
Merge pull request #1671 from hypothesis/1300-fix-chrome-deployment

Fix chrome extension build