These assertion counts were removed (accidentally?) by bug 1321127, effectively
not tracking assertion count mismatches in the reftest harness and instead
relying on mozharness to fail tasks based on the logged error messages.
Restoring the counts ensures:
 - the reftest summary includes accurate assertion counts like
   REFTEST INFO | Unexpected: 12 (..., 11 unexpected asserts, ...)
   REFTEST INFO | Known problems: 64 (..., 31 known asserts, ...)
 - assertion mismatches cause the harness to exit with an error code so
   that the job fails even if the log parsing is broken (bug 1587139)
   or the tests are being run locally with mach.

Differential Revision: https://phabricator.services.mozilla.com/D48594

--HG--
extra : moz-landing-system : lando