WebRTC AGC (Automatic Gain Control)

Here is the sequence of operations to be used for Webrtc_AGC:

1. Create AGC: WebRtcAgc_Create
2. Initialize AGC: WebRtcAgc_Init
3. Set Config: WebRtcAgc_set_config
4. Initialize capture_level = 0
5. For kAgcModeAdaptiveDigital, invoke VirtualMic: WebRtcAgc_VirtualMic
6. Process Buffer with capture_level: WebRtcAgc_Process
7. Get the out capture level returned from WebRtcAgc_Process and set it to capture_level
8. Repeat 5 to 7 for the audio buffers
9. Destroy the AGC: WebRtcAgc_Free

Check webrtc/modules/audio_processing/gain_control_impl.cc for reference.