Make GetConfig() part of the AudioProcessing interface

BUG=chromium:708475
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_chromium_rel_ng

Review-Url: https://codereview.webrtc.org/2802603003
Cr-Commit-Position: refs/heads/master@{#17540}
diff --git a/webrtc/modules/audio_processing/include/audio_processing.cc b/webrtc/modules/audio_processing/include/audio_processing.cc
index 43b2c27..312d0cb 100644
--- a/webrtc/modules/audio_processing/include/audio_processing.cc
+++ b/webrtc/modules/audio_processing/include/audio_processing.cc
@@ -31,5 +31,8 @@
 
 Beamforming::~Beamforming() {}
 
+AudioProcessing::Config AudioProcessing::GetConfig() const {
+  return AudioProcessing::Config();
+}
 
 }  // namespace webrtc