This clarifies dependencies and makes it easier to customize builds for different binaries. Also adds BUILD files in aec/ and aecm/. Moves unit tests to their own target, which subjects them to Chromium Clang style checks. The CL contains a fix for a thusly induced warning. Bug: webrtc:9488 Change-Id: I77b680b42a4dccc5f025005e0890f60b4eaf2961 Reviewed-on: https://webrtc-review.googlesource.com/87304 Commit-Queue: Sam Zackrisson <saza@webrtc.org> Reviewed-by: Alex Loiko <aleloi@webrtc.org> Cr-Commit-Position: refs/heads/master@{#23887}