[Beta] Have Cirrus build index for regexes

This causes Cirrus to build a trigram index on the page source to accelerate
the insource:// operator.  Its a noop before
If9fcb6a03c23e8abaf59b5ddfadab051263dac33 is merged.

Change-Id: Ia9ee3ddc7d591a6a85b644627c912b7ffdcc5b6e