Introduced new scheme for controlling the functionality inside the audio processing module

webrtc/modules/audio_processing/level_controller/level_controller.cc

Index: webrtc/modules/audio_processing/level_controller/level_controller.cc
diff --git a/webrtc/modules/audio_processing/level_controller/level_controller.cc b/webrtc/modules/audio_processing/level_controller/level_controller.cc
index 2294396607505f86511e83f12f110a8a636601bf..2fb34851e68b07d77d675f481b85922099d66e4b 100644
--- a/webrtc/modules/audio_processing/level_controller/level_controller.cc
+++ b/webrtc/modules/audio_processing/level_controller/level_controller.cc
@@ -262,4 +262,23 @@ void LevelController::Process(AudioBuffer* audio) {
                         audio->channels_f()[0], *sample_rate_hz_, 1);
 }
 
+std::string LevelController::ToString(
+    const AudioProcessing::Config::LevelController& config) {
+  std::stringstream ss;
+  ss << "LevelController config: "

[the sun, 2016/09/07 15:49:39]

Please use the json-ish way of string serialization that is used elsewhere for
configs. See e.g. AudioReceiveStream::Config::ToString(). (I'm missing enclosing
"{" "}".

[peah-webrtc, 2016/09/08 09:13:49]

Good suggestion!
Done.

[the sun, 2016/09/08 09:45:55]

Add a test for the function too.

[peah-webrtc, 2016/09/08 19:34:24]

Done.

+     << "enabled=" << (config.enabled ? "true" : "false");
+  return ss.str();
+}
+
+AudioProcessing::Config::LevelController LevelController::DefaultConfig() {
+  AudioProcessing::Config::LevelController config;
+  config.enabled = false;

[hlundin-webrtc, 2016/09/07 21:13:05]

The default config should be the one you get from the constructor, imho. Thus,
you should only need to return AudioProcessing::Config::LevelController(). But,
as I alluded to previously, I don't think this method is needed.

[peah-webrtc, 2016/09/08 09:13:49]

You are probably correct that it is not needed, and very likely this should be
changed anyway to something along the FixConfig approach I mentioned in the
other comment. . But I cannot see how to use the constructor in
AudioProcessing::Config::LevelController() to produce default parameters without
moving logic from within the level controller out to the
audio_processing_impl.cc file. 

The only exception would be if the default value would be everything off.

WDYT? 
Should I change this to AudioProcessing::Config::LevelController
LevelController::FixConfig(AudioProcessing::Config::LevelController config),
or should I let the constructor  AudioProcessing::Config::LevelController()
produce a default parameter set where everything is off?

+  return config;
+}
+
+bool LevelController::Validate(
+    const AudioProcessing::Config::LevelController& config) {
+  return true;
+}
+
 }  // namespace webrtc