stagefright: Add FLAC support to MatroskaExtractor

Change-Id: Ib1b7d7e6fed617404eb5581a5f87ab67531f5bb8
stagefright: Support HEVC tracks in Matroska containers

 * Pass the HVCC atom to Stagefright.

Change-Id: I7fdca25e20b9051925936a34e594808b18a3a3bd