For live streams, we cannot assume that the input decoding timestamp
starts from zero.
Also don't overwrite |normalize_presentation_timestamp| if the user
does not want to enable it for on-demand profile.
Change-Id: I1abe7926e0b25eb11dee021be964d126484d4036
This CL also includes two related changes:
1. Support serialization of raw PSSH box;
2. Refactor segmenter interface a bit.
Change-Id: I668aa01a5a5ff524ad6fe74976339a3fd499120a