Added a kEchoCancellation constraint to turn off the audio processing.

content/renderer/media/media_stream_audio_processor_options.h

Index: content/renderer/media/media_stream_audio_processor_options.h
diff --git a/content/renderer/media/media_stream_audio_processor_options.h b/content/renderer/media/media_stream_audio_processor_options.h
index 3ad41100b4c78f1157519b2598df4435fd692f1b..bac643ee2170e72ddf779ac94e641655e474c612 100644
--- a/content/renderer/media/media_stream_audio_processor_options.h
+++ b/content/renderer/media/media_stream_audio_processor_options.h
@@ -30,6 +30,18 @@ class RTCMediaConstraints;
 using webrtc::AudioProcessing;
 using webrtc::MediaConstraintsInterface;
 
+// Constraint keys used by audio processing.
+extern const char kEchoCancellation[];
+extern const char kGoogEchoCancellation[];
+extern const char kGoogExperimentalEchoCancellation[];
+extern const char kGoogAutoGainControl[];
+extern const char kGoogExperimentalAutoGainControl[];
+extern const char kGoogNoiseSuppression[];
+extern const char kGoogExperimentalNoiseSuppression[];
+extern const char kGoogHighpassFilter[];
+extern const char kGoogTypingNoiseDetection[];
+extern const char kGoogAudioMirroring[];
+
 // Merge |constraints| with |kDefaultAudioConstraints|. For any key which exists
 // in both, the value from |constraints| is maintained, including its
 // mandatory/optional status. New values from |kDefaultAudioConstraints| will
@@ -48,8 +60,13 @@ bool NeedsAudioProcessing(const blink::WebMediaConstraints& constraints,
 // Returns true if the key is found and has a valid boolean value; Otherwise

[perkj_chrome, 2014/04/11 11:45:04]

"and has a valid boolean value that is true."

I think this is a bit confusing. How about having the return value mean that the
key exist and have an out parameter with the actual value of it? 

[no longer working on chromium, 2014/04/11 16:47:05]

Returning two values might not be the best.

The usage of GetPropertyFromConstraints() is to tell the property is true or
not.
If the |key| exists, then it returns the value; otherwise returns the default
value of the default value.

I changed the comment and hope it is clear.

 // false.

[perkj_chrome, 2014/04/11 11:45:04]

document |effects|

[no longer working on chromium, 2014/04/11 16:47:05]

Added comment to the constructor of the new MediaAudioConstraints class.

 bool GetPropertyFromConstraints(

[perkj_chrome, 2014/04/11 11:45:04]

I think you have to but these functions in class scope. The names are two
general to add as a function in content.

[no longer working on chromium, 2014/04/11 16:47:05]

Done.

-    const MediaConstraintsInterface* constraints,
-    const std::string& key);
+    const blink::WebMediaConstraints& constraints,
+    const std::string& key,
+    int effects);
+
+// Returns true if all the mandatory constraints in |constraints| are valid;
+// Otherwise return false.
+bool IsValid(const blink::WebMediaConstraints& constraints);

[perkj_chrome, 2014/04/11 11:45:04]

dito - this is audio specific.

[no longer working on chromium, 2014/04/11 16:47:05]

Done.

 
 // Enables the echo cancellation in |audio_processing|.
 void EnableEchoCancellation(AudioProcessing* audio_processing);