Monitor returns number of available workers per model.
Base64 is used for pcm encoding.
SpeechRecognition.js encodes pcm data to base64.
PCM data is encoded using utf8 characters.
Benchmark of pcm serialization created.

Results of the benchmark are:

  raw file size |  56146 |
----------------+--------+-------
 bytes_protobuf	|  56118 | 0.999x
         base64	|  74872 | 1.333x
 array_protobuf	|  94157 | 1.677x
     json_array	| 158590 | 2.824x
           utf8	| 281766 | 5.018x
Base64 is used for pcm serialization.

This reverts commit 6f9b6d21fb3111332d594a796e2df30516390a18.