The method currently has two ways of operating with a complicated
contract:
1. outputBuffer == null -> sets a new outputBuffer and starts
draining it as far as possible.
2. outputBuffer != null -> continues draining a previous buffer,
requires that the input parameter is the same as outputBuffer.
This contract can be made cleaner by splitting the logic into
(1) setting a new output buffer and (2) draining the output buffer.
Only one parameter is needed for each method and there is no
requirement to pass in the same argument as before because we already
know what we are draining. This also means the caller of the method
doesn't have to keep track of the actual outputBuffer, allowing
further processing steps in the future that change the drained
instance.
PiperOrigin-RevId: 663316251
b58a1d16f7