method in the AEC into two methods.
This CL is step towards simplifying the AEC code, making it
more modifiable and modular.
The changes should be bitexact.
BUG=webrtc:5201, webrtc:5298
Review-Url: https://codereview.webrtc.org/1943753002
Cr-Commit-Position: refs/heads/master@{#12656}