In our text to mp4 tests, we were only checking if the times on
the samples lined-up with what we were expecting.
We want to check that text sample contents (ids, settings, and
payloads) were correctly merged into a single media sample. To
verify this, we now check if the sample ids appear in the
media sample.
Change-Id: Ica1a85a14e7b116275e3571332b2e90d7bc44c45