Revert "Revert "Merge pull request #1587 from guardian/ab-most-viewed-by-referrer""

This reverts commit 876060f8fa9f00bc3536053353148cf04a5ada46.
Fix js warning
Merge remote-tracking branch 'origin/master' into kc-fix-js

Conflicts:
	common/app/conf/switches.scala
Merge pull request #1616 from guardian/kc-fix-js

Reinstate reverted change