This Cl is the first step of a 3-step process to trick the build system of a
webrtc dependency into not failing.
The second step will be to register this folder in the dependency
build system. It cannot be done first, because there must be a GN
dependency from some existing target to a target in the new folder.
The third step is to land https://codereview.webrtc.org/2424173003, in
which the webrtc/audio/utility is used.
When a new folder with a publicly visible header is added, the build
files of said build system must be manually updated to register the
new folder.
BUG=webrtc:6548
Review-Url: https://codereview.webrtc.org/2532403003
Cr-Commit-Position: refs/heads/master@{#15299}
939e08f5f4