Added a kEchoCancellation constraint to turn off the audio processing.

content/renderer/media/media_stream_constraints_util.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_MEDIA_STREAM_CONSTRAINTS_UTIL_H_
+#define CONTENT_RENDERER_MEDIA_MEDIA_STREAM_CONSTRAINTS_UTIL_H_
+
+#include <string>
+
+namespace blink {
+class WebMediaConstraints;
+class WebString;
+}
+
+namespace content {
+
+// Method to get boolean value of constraint with |key| from constraints.
+// Returns true if the constraint is specified in either mandatory or optional
+// constraints.
+bool GetConstraintValueAsBoolean(const blink::WebMediaConstraints& constraints,
+                                 const std::string& key,
+                                 bool* value);
+
+// Method to get int value of constraint with |key| from constraints.
+// Returns true if the constraint is specified in either mandatory or Optional
+// constraints.
+bool GetConstraintValueAsInteger(const blink::WebMediaConstraints& constraints,
+                                 const std::string& key,
+                                 int* value);
+
+// Method to get std::string value of constraint with |key| from constraints.
+// Returns true if the constraint is specified in either mandatory or Optional
+// constraints.
+bool GetConstraintValueAsString(const blink::WebMediaConstraints& constraints,
+                                const std::string& key,
+                                std::string* value);
+
+// Method to get boolean value of constraint with |key| from the
+// mandatory constraints.
+bool GetMandatoryConstraintValueAsBoolean(
+    const blink::WebMediaConstraints& constraints,
+    const std::string& name,
+    bool* value);
+
+// Method to get int value of constraint with |key| from the
+// mandatory constraints.
+bool GetMandatoryConstraintValueAsInteger(
+    const blink::WebMediaConstraints& constraints,
+    const std::string& name,
+    int* value);
+
+// Method to get bool value of constraint with |key| from the
+// optional constraints.
+bool GetOptionalConstraintValueAsBoolean(
+    const blink::WebMediaConstraints& constraints,
+    const std::string& name,
+    bool* value);
+
+// Method to get int value of constraint with |key| from the
+// optional constraints.
+bool GetOptionalConstraintValueAsInteger(
+    const blink::WebMediaConstraints& constraints,
+    const std::string& name,
+    int* value);
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_MEDIA_STREAM_CONSTRAINTS_UTIL_H_