Adding opt out and previews type information to DRP pingback

This CL adds the previews type that was shown for a page load and also
reports when a page load was an opt out (clicked show original). Due to
backgrounding behavior, when app background occurs or there is not a
previews shown a third opt out state of unknown is reported. LoFi page
state is determined if any subresources were LoFi images. Lite page uses
the main resource to determine preview state.


Cr-Commit-Position: refs/heads/master@{#466376}
31 files changed