test: Fix offline test failures with MediaCap
test: Fix offline test failures with MediaCap

Because our MediaCapabilities integration adds decoding info to each
variant, we need to be careful to reset this info on variants that are
cached and persist between tests and between manifest parser
instances.  This ensures that these unusual test variants will not
have persistent decoding infos from MediaCapabilities.

For encrypted content, the decoding info contains negotiated EME
information which varies based on the chosen key system and whether
the content will be streamed or stored offline.  If one test loads the
content for streaming, then another test loads the same content for
offline storage, the second test would encounter the cached decoding
info from the first test, and the negotatied key system would not be
set up for the correct session types.  This would lead to a test
failure.  This sort of failure would not be seen in real playback
(since no supported manifest parser would ever cache variants).

By resetting variant.decodingInfos when the fake manifest parser is
stopped, we ensure that each test gets a clean slate (as would happen
with a real parser), and the correct decodingInfos show up for each
part of each test case.

Change-Id: I73aea2e5144723512eb460d866ac9620937492bc

tvoli/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player