Added a bitexactness test for the gain controller in the audio processing module.

BUG=webrtc:5339

Review URL: https://codereview.webrtc.org/1812433002

Cr-Original-Commit-Position: refs/heads/master@{#12124}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: a49dc36976da44f3d6d75aed2dcab93fe14fc3a0
2 files changed