Introduce finer-grained Media Viewer EventLogging sampling

Related code change:  I3966bf5dfe9ed607bda8e87f3b1924de37716dcf

Change-Id: I5c78d34fd6423cb6f8b599e2e8e2d0f4492a1b54
Mingle: https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/619
Merge "Introduce finer-grained Media Viewer EventLogging sampling"