Bug 1109457 - Add persistent session to our ClearKey CDM. r=edwin
Bug 1109457 - Use Contains instead of std.find to detect whether we have keys in gmp-clearkey, and don't overwrite old decryptors when we get a new key. r=edwin.
Bug 1109457 - Prevent potential for Join()ing a pointer held in free'd memory in gmp-clearkey. r=edwin