[niconico] Support for HLS-only videos

[hakatashi]

Checklist

• I'm reporting a site feature request
• I've verified that I'm running youtube-dl version 2019.09.28
• I've searched the bugtracker for similar site feature requests including closed ones

Description

Recently niconico introduced support for HLS videos and now some of the new licensed videos are provided only in HLS format.

Examples:

• https://www.nicovideo.jp/watch/1562727729
• https://www.nicovideo.jp/watch/so35376541

Since yt-dl is currently not supporting downloading HLS videos of niconico, these URLs fail to download video infos and emit the following errors.

$ youtube-dl --verbose -u ### -p ### https://www.nicovideo.jp/watch/1562727729
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['--verbose', '-u', 'PRIVATE', '-p', 'PRIVATE', 'https://www.nicovideo.jp/watch/1562727729']
[debug] Encodings: locale cp932, fs mbcs, out cp65001, pref cp932
[debug] youtube-dl version 2019.09.28
[debug] Python version 3.4.4 (CPython) - Windows-10-10.0.18362
[debug] exe versions: ffmpeg 2.8.4, ffprobe 3.4.1, rtmpdump 2.3
[debug] Proxy map: {'no': '192.168.99.100'}
[niconico] Logging in
[niconico] 1562727729: Downloading webpage
[niconico] 1562727729: Downloading JSON metadata for h264_720p-aac_192kbps
ERROR: Unable to download JSON metadata: HTTP Error 403: Forbidden (caused by HTTPError()); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; type  youtube-dl -U  to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
  File "C:\Users\dst\AppData\Roaming\Build archive\youtube-dl\ytdl-org\tmpyi91grvc\build\youtube_dl\extractor\common.py", line 627, in _request_webpage
  File "C:\Users\dst\AppData\Roaming\Build archive\youtube-dl\ytdl-org\tmpyi91grvc\build\youtube_dl\YoutubeDL.py", line 2237, in urlopen

  File "C:\Python\Python34\lib\urllib\request.py", line 470, in open
  File "C:\Python\Python34\lib\urllib\request.py", line 580, in http_response
  File "C:\Python\Python34\lib\urllib\request.py", line 508, in error
  File "C:\Python\Python34\lib\urllib\request.py", line 442, in _call_chain
  File "C:\Python\Python34\lib\urllib\request.py", line 588, in http_error_default

For technical details, HLS-only videos have metadata with api_data['video']['dmcInfo']['session_api']['protocols'] == ['hls'], not ['http', 'hls'].