Added a kEchoCancellation constraint to turn off the audio processing.

content/renderer/media/mock_media_constraint_factory.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_RENDERER_MEDIA_MOCK_MEDIA_STREAM_CONSTRAINT_H_
 #define CONTENT_RENDERER_MEDIA_MOCK_MEDIA_STREAM_CONSTRAINT_H_
 
 #include <string>
 #include <vector>
 
 #include "third_party/WebKit/public/platform/WebMediaConstraints.h"
 
 namespace content {
 
 class MockMediaConstraintFactory {
  public:
   MockMediaConstraintFactory();
   ~MockMediaConstraintFactory();
 
   blink::WebMediaConstraints CreateWebMediaConstraints();
   void AddMandatory(const std::string& key, int value);
   void AddMandatory(const std::string& key, double value);
+  void AddMandatory(const std::string& key, const std::string& value);
   void AddOptional(const std::string& key, int value);
   void AddOptional(const std::string& key, double value);
+  void AddOptional(const std::string& key, const std::string& value);
   void DisableDefaultAudioConstraints();
 
  private:
   std::vector<blink::WebMediaConstraint> mandatory_;
   std::vector<blink::WebMediaConstraint> optional_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_MOCK_MEDIA_STREAM_CONSTRAINT_H_