A ClosableStringSink extends the StringSink interface by adding a
close
method.
sink
and a callback
onClose
which is invoked when the returned instance is closed.
this
and flushes any outstanding data.
obj
to a String by invoking Object.toString and
adds the result to this
.
objects
and writes them in sequence.
charCode
to this
. [...]
obj
to a String by invoking Object.toString and
adds the result to this
, followed by a newline.