Add examples for decodingInfo()

[mounirlamouri]

Following up from a TPAC action, see https://www.w3.org/2019/09/18-mediawg-minutes.html#item09

We want to add examples for decodingInfo(). Today, there are only encodingInfo() examples and we got feedback that more examples would be welcomed.

[wilaw]

Here is a script example for decodingInfo() which matches that for encodingInfo()

<script>
const configuration = {
      type : 'media-source',
      video : {
        contentType : 'video/mp4;codecs=avc1.640028',
        width : 640,
        height : 360,
        bitrate : 2000,
        framerate : 29.97
    }
  };
  navigator.mediaCapabilities.decodingInfo(configuration)
      .then((result) => {
        console.log('Decoding of ' + configuration.video.contentType + ' is'
            + (result.supported ? '' : ' NOT') + ' supported,'
            + (result.smooth ? '' : ' NOT') + ' smooth and'
            + (result.powerEfficient ? '' : ' NOT') + ' power efficient');
      })
      .catch((err) => {
        console.error(err, ' caused decodingInfo to throw an error');
      });
</script>

[chrisn]

I created PR #151 to add @wilaw's example. We should also consider adding examples including audio and encryption configurations.

[chrisn]

I'll close this, as we have #197 for adding a MediaCapabilitiesKeySystemConfiguration example.