This CL introduces the handling of multiple microphone channels in the EchoRemover layer. The implementation is done such as to support an arbitrary number of channels in a way that balances stack and heap-space usage. Bug: webrtc:10913 Change-Id: I475369de6c463b8fe2d7e53799d7322eefb6938f Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/151647 Commit-Queue: Per Åhgren <peah@webrtc.org> Reviewed-by: Sam Zackrisson <saza@webrtc.org> Cr-Commit-Position: refs/heads/master@{#29140}