the previously specified setting is changed if it is specified to be changed,
and otherwise the previously specified setting is kept as it is.
This CL replicates this functionality for the way that the new APM
parameter scheme is used.
BUG=webrtc::6220, webrtc::6296, webrtc::6297, webrtc::6181, webrtc::5298
Review-Url: https://codereview.webrtc.org/2489343002
Cr-Commit-Position: refs/heads/master@{#15167}