Added a kEchoCancellation constraint to turn off the audio processing.

content/renderer/media/mock_media_constraint_factory.cc

Index: content/renderer/media/mock_media_constraint_factory.cc
diff --git a/content/renderer/media/mock_media_constraint_factory.cc b/content/renderer/media/mock_media_constraint_factory.cc
index 99d9f56244b49030173e76e88303b1c6eb246355..5d5e7d3998170d04c6e9a06f7c2fe5c745831bfb 100644
--- a/content/renderer/media/mock_media_constraint_factory.cc
+++ b/content/renderer/media/mock_media_constraint_factory.cc
@@ -37,6 +37,12 @@ void MockMediaConstraintFactory::AddMandatory(const std::string& key,
       base::UTF8ToUTF16(base::DoubleToString(value))));
 }
 
+void MockMediaConstraintFactory::AddMandatory(const std::string& key,
+                                              const std::string& value) {
+  mandatory_.push_back(blink::WebMediaConstraint(
+      base::UTF8ToUTF16(key), base::UTF8ToUTF16(value)));
+}
+
 void MockMediaConstraintFactory::AddOptional(const std::string& key,
                                              int value) {
   optional_.push_back(blink::WebMediaConstraint(base::UTF8ToUTF16(key),
@@ -50,6 +56,12 @@ void MockMediaConstraintFactory::AddOptional(const std::string& key,
       base::UTF8ToUTF16(base::DoubleToString(value))));
 }
 
+void MockMediaConstraintFactory::AddOptional(const std::string& key,
+                                             const std::string& value) {
+  optional_.push_back(blink::WebMediaConstraint(
+      base::UTF8ToUTF16(key), base::UTF8ToUTF16(value)));
+}
+
 void MockMediaConstraintFactory::DisableDefaultAudioConstraints() {
   static const char* kDefaultAudioConstraints[] = {
       webrtc::MediaConstraintsInterface::kEchoCancellation,