fix(hls): Recognize the types of mp4a and mp4v extensions

The HLS content linked in shaka-project#2907 uses the .mp4a extension for audio
segments, so it is helpful for us to be able to recognize the types of
these segments.  This adds both .mp4a and .mp4v to the extension maps
in the HLS parser.

Change-Id: I8f2e126691e552c34ff5da027fca32ed925a2bdf

lib/hls/hls_parser.js

@@ -2727,6 +2727,7 @@ shaka.hls.HlsParser.CODEC_REGEXPS_BY_CONTENT_TYPE_ = {
  */
 shaka.hls.HlsParser.AUDIO_EXTENSIONS_TO_MIME_TYPES_ = {
   'mp4': 'audio/mp4',
+  'mp4a': 'audio/mp4',
   'm4s': 'audio/mp4',
   'm4i': 'audio/mp4',
   'm4a': 'audio/mp4',
@@ -2763,6 +2764,7 @@ shaka.hls.HlsParser.RAW_FORMATS_ = [
  */
 shaka.hls.HlsParser.VIDEO_EXTENSIONS_TO_MIME_TYPES_ = {
   'mp4': 'video/mp4',
+  'mp4v': 'video/mp4',
   'm4s': 'video/mp4',
   'm4i': 'video/mp4',
   'm4v': 'video/mp4',