Attempt to sniff raw mp3 with no id3 tag by looking for a header
followed by a second header at the expected offset from the packet
length.
Adds mp3 sniffing with and without id3 tags to the mediasniffer
xpcshell tests. These files are truncated to 512 bytes. Our method
can require up to 1.5k of data, but these have 208/209 byte packets
so sniffing still works.
notags-bad.mp3 has a corrupt header, and verifies sniffing fails.
notags-scan.mp3 has garbage before the header, and verifies sniffing fails.
he_free.mp is a vbr test vector which isn't sniffable with this method.
fl10.mp2 is an mp2 file, and verifies sniffing fails.
ff-inst.exe verifies bug 875769 doesn't regress.
f5e4f4e145