Issue 6809 - Implement hide-if-contains snippet

[Manish Jethani, 2018-07-23 23:15:32]

Patch Set 1

I'll update the Trac issue, but this is a complement to the
hide-if-shadow-contains snippet. Sometimes the ad label is not in a shadow root,
it is outside. Normally this job would be done by an element hiding emulation
filter (it works), but it's too slow to apply the filter (#6804). This is a
better option that keeps it consistent.

This implementation is not the most efficient, but it should serve the intended
purpose for now.

[Manish Jethani, 2018-07-26 10:34:57]

Since #6804 is going to be more challenging to do, we should get this snippet
into this release.

[hub, 2018-07-26 12:05:57]

LGTM, but what the difference with :-abp-contains() ?

[Manish Jethani, 2018-07-26 12:10:51]

On 2018/07/26 12:05:57, hub wrote:
> LGTM, but what the difference with :-abp-contains() ?

Thanks!

:-abp-contains() runs only after the DOMContentLoaded event (see #6804), by
which time the ad has already been displayed for a second or two. When the ad is
hidden, everything shifts on the page. Overall this is a bad user experience.

Eventually we should address this in #6804 and then remove this snippet.