Added a kEchoCancellation constraint to turn off the audio processing.

content/renderer/media/media_stream_constraints_util.cc

+// 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.
+
+#include "content/renderer/media/media_stream_constraints_util.h"
+
+#include "base/strings/string_number_conversions.h"
+#include "base/strings/utf_string_conversions.h"
+#include "third_party/WebKit/public/platform/WebMediaConstraints.h"
+#include "third_party/WebKit/public/platform/WebString.h"
+
+namespace content {
+
+bool GetConstraintValue(const blink::WebMediaConstraints& constraints,
+                        const std::string& key,
+                        bool* value) {
+  int constraint_value = 0;
+  if (!GetConstraintValue(constraints, key, &constraint_value))
+    return false;
+
+  *value = static_cast<bool>(constraint_value);
+  return true;
+}
+
+bool GetConstraintValue(const blink::WebMediaConstraints& constraints,
+                        const std::string& key,
+                        int* value) {
+  return GetMandatoryConstraintValue(constraints, key, value) ||
+         GetOptionalConstraintValue(constraints, key, value);
+}
+
+bool GetConstraintValue(const blink::WebMediaConstraints& constraints,
+                        const std::string& key,
+                        std::string* value) {
+  blink::WebString value_str;
+  if (!constraints.getMandatoryConstraintValue(base::UTF8ToUTF16(key),
+                                               value_str) &&
+      !constraints.getOptionalConstraintValue(base::UTF8ToUTF16(key),
+                                              value_str)) {
+    return false;
+  }
+
+  *value = value_str.utf8();
+  return true;
+}
+
+bool GetMandatoryConstraintValue(const blink::WebMediaConstraints& constraints,
+                                 const std::string& key,
+                                 int* value) {
+  blink::WebString value_str;
+  if (!constraints.getMandatoryConstraintValue(base::UTF8ToUTF16(key),
+                                               value_str)) {
+    return false;
+  }
+
+  return base::StringToInt(value_str.utf8(), value);
+}
+
+bool GetOptionalConstraintValue(const blink::WebMediaConstraints& constraints,
+                                const std::string& key,
+                                int* value) {
+  blink::WebString value_str;
+  if (!constraints.getOptionalConstraintValue(base::UTF8ToUTF16(key),
+                                              value_str)) {
+    return false;
+  }
+
+  return base::StringToInt(value_str.utf8(), value);
+}
+
+}  // namespace content