Impression events via EventLogging

Authored by AndyRussG on Feb 6 2018, 5:38 AM.


Impression events via EventLogging

Adds impression events, expected to supersede recording impressions
via beacon/impression. Currently implemented alongside that feature.

Provides a new mixin to control impression event sample rates on a
per-campaign basis.

Instead of loading EventLogging modules client-side, we construct a
URL that should be the same as the one sent by EventLogging
JavaScript. Must coordinate with that extension to ensure the URL
we send remains correct.

Must coordinate with the CentralNoticeImpression EventLogging schema.

Also moves EventLogging schema configuration to extension.json.

Bug: T185932
Change-Id: I6052ebd58a0137d8f6beded1f78162eb02b75649