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 {
+
+namespace {
+
+// Convert a string ("true", "false") to a boolean.
+bool ConvertStringToBoolean(const std::string& string, bool* value) {
+  static const char kValueTrue[] = "true";
+  static const char kValueFalse[] = "false";
+
+  *value = (string == kValueTrue);
+  return *value || (string == kValueFalse);
+}
+
+}  // namespace
+
+bool GetConstraintValueAsBoolean(const blink::WebMediaConstraints& constraints,
+                                 const std::string& key,
+                                 bool* value) {
+  return GetMandatoryConstraintValueAsBoolean(constraints, key, value) ||
+         GetOptionalConstraintValueAsBoolean(constraints, key, value);
+}
+
+bool GetConstraintValueAsInteger(const blink::WebMediaConstraints& constraints,
+                                 const std::string& key,
+                                 int* value) {
+  return GetMandatoryConstraintValueAsInteger(constraints, key, value) ||
+         GetOptionalConstraintValueAsInteger(constraints, key, value);
+}
+
+bool GetConstraintValueAsString(const blink::WebMediaConstraints& constraints,
+                                const std::string& key,
+                                std::string* value) {
+  blink::WebString value_str;
+  base::string16 key_16 = base::UTF8ToUTF16(key);
+  if (!constraints.getMandatoryConstraintValue(key_16, value_str) &&
+      !constraints.getOptionalConstraintValue(key_16, value_str)) {
+    return false;
+  }
+
+  *value = value_str.utf8();
+  return true;
+}
+
+bool GetMandatoryConstraintValueAsBoolean(
+    const blink::WebMediaConstraints& constraints,
+    const std::string& key,
+    bool* value) {
+  blink::WebString value_str;
+  if (!constraints.getMandatoryConstraintValue(base::UTF8ToUTF16(key),
+                                               value_str)) {
+    return false;
+  }
+
+  return ConvertStringToBoolean(value_str.utf8(), value);
+}
+
+bool GetMandatoryConstraintValueAsInteger(
+    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);

[perkj_chrome, 2014/05/08 13:42:24]

Humm - you are aware that there is a difference between that a key doesn't exist
and that it can't be translated?

If the constraint is mandatory, the call should fail if it exists but the value
can not be applied. If it does not exist everything should be per the default
value.
If its optional - it is probably correct to just ignore that its there at all.

So parsing errors and that a value doen't exist is not necessarily the same
thing.

[no longer working on chromium, 2014/05/12 14:39:09]

Added a GetMandatoryConstraintValueAsBoolean(key) in
MediaAudioConstraints::IsValid() check so that we know all the mandatory
constraints are valid.

+}
+
+bool GetOptionalConstraintValueAsBoolean(
+    const blink::WebMediaConstraints& constraints,
+    const std::string& key,
+    bool* value) {
+  blink::WebString value_str;
+  if (!constraints.getOptionalConstraintValue(base::UTF8ToUTF16(key),
+                                              value_str)) {
+    return false;
+  }
+
+  return ConvertStringToBoolean(value_str.utf8(), value);
+}
+
+bool GetOptionalConstraintValueAsInteger(
+    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