Properly error check calls to AudioProcessing.

Checks must be made with "!= 0", not "== -1". Additionally:
* Clean up the function calling into AudioProcessing.
* Remove the unused _noiseWarning.
* Make the other warnings bool.

BUG=chromium:178040

Review URL: https://webrtc-codereview.appspot.com/1147004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@3590 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/webrtc/modules/audio_processing/include/audio_processing.h b/webrtc/modules/audio_processing/include/audio_processing.h
index 192b539..6f09667 100644
--- a/webrtc/modules/audio_processing/include/audio_processing.h
+++ b/webrtc/modules/audio_processing/include/audio_processing.h
@@ -285,8 +285,8 @@
 
   // Sets the difference between the number of samples rendered and captured by
   // the audio devices since the last call to |ProcessStream()|. Must be called
-  // if and only if drift compensation is enabled, prior to |ProcessStream()|.
-  virtual int set_stream_drift_samples(int drift) = 0;
+  // if drift compensation is enabled, prior to |ProcessStream()|.
+  virtual void set_stream_drift_samples(int drift) = 0;
   virtual int stream_drift_samples() const = 0;
 
   enum SuppressionLevel {