Implementing WebRTC Auto Gain Control (AGC) test (minus verification).
This implements the test scaffolding. We still need a tool to analyze
the audio energy of the output file and ensure it matches the energy
level of the input file.
The test will be disabled for now until the tool is in place.
The next patches will be to wire up the tool and, after that, write
more exciting tests which verify the AGC actually kicks in and adjusts
the level (this test just ensures it doesn't zero the volume level).
BUG=303259
Review URL: https://codereview.chromium.org/
753993002
Cr-Commit-Position: refs/heads/master@{#307448}