DataChannel 
    Java wrapper for a C++ DataChannelInterface.
Functions
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                  Return the number of bytes of application data (UTF-8 text and binary data) that have been queued using SendBuffer but have not yet been transmitted to the network.
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                  Register `observer`, replacing any previously-registered observer.
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                  Send `data` to the remote peer; return success.
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                  Unregister the (only) observer.