Added a kEchoCancellation constraint to turn off the audio processing.

content/renderer/media/media_stream_video_source.cc

Index: content/renderer/media/media_stream_video_source.cc
diff --git a/content/renderer/media/media_stream_video_source.cc b/content/renderer/media/media_stream_video_source.cc
index 28cc3e2e73948d731f3be9ba4f114f79536926b8..612be36f022250577b9c4efce66cea35ff9024ce 100644
--- a/content/renderer/media/media_stream_video_source.cc
+++ b/content/renderer/media/media_stream_video_source.cc
@@ -10,6 +10,7 @@
 
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
+#include "content/renderer/media/media_stream_constraints_util.h"
 #include "content/renderer/media/media_stream_dependency_factory.h"
 #include "content/renderer/media/media_stream_video_track.h"
 #include "content/renderer/media/webrtc/webrtc_video_capturer_adapter.h"
@@ -203,34 +204,22 @@ media::VideoCaptureFormats FilterFormats(
   return candidates;
 }
 
-bool GetConstraintValue(const blink::WebMediaConstraints& constraints,
-                        bool mandatory, const blink::WebString& name,
-                        int* value) {
-  blink::WebString value_str;
-  bool ret = mandatory ?
-      constraints.getMandatoryConstraintValue(name, value_str) :
-      constraints.getOptionalConstraintValue(name, value_str);
-  if (ret)
-    base::StringToInt(value_str.utf8(), value);
-  return ret;
-}
-
 // Retrieve the desired max width and height from |constraints|.
 void GetDesiredMaxWidthAndHeight(const blink::WebMediaConstraints& constraints,
                                  int* desired_width, int* desired_height) {
-  bool mandatory = GetConstraintValue(constraints, true,
-                                      MediaStreamVideoSource::kMaxWidth,
-                                      desired_width);
-  mandatory |= GetConstraintValue(constraints, true,
-                                  MediaStreamVideoSource::kMaxHeight,
-                                  desired_height);
+  bool mandatory = GetMandatoryConstraintValue(
+      constraints, MediaStreamVideoSource::kMaxWidth, desired_width);
+  mandatory |= GetMandatoryConstraintValue(
+      constraints, MediaStreamVideoSource::kMaxHeight, desired_height);
+  // Skip the optional constraints if any of the mandatory constraint is
+  // specified.
   if (mandatory)
     return;
 
-  GetConstraintValue(constraints, false, MediaStreamVideoSource::kMaxWidth,
-                     desired_width);
-  GetConstraintValue(constraints, false, MediaStreamVideoSource::kMaxHeight,
-                     desired_height);
+  GetOptionalConstraintValue(constraints, MediaStreamVideoSource::kMaxWidth,
+                             desired_width);
+  GetOptionalConstraintValue(constraints, MediaStreamVideoSource::kMaxHeight,
+                             desired_height);
 }
 
 const media::VideoCaptureFormat& GetBestFormatBasedOnArea(
@@ -324,10 +313,11 @@ void MediaStreamVideoSource::AddTrack(
       // Tab capture and Screen capture needs the maximum requested height
       // and width to decide on the resolution.
       int max_requested_width = 0;
-      GetConstraintValue(constraints, true, kMaxWidth, &max_requested_width);
+      GetMandatoryConstraintValue(constraints, kMaxWidth, &max_requested_width);
 
       int max_requested_height = 0;
-      GetConstraintValue(constraints, true, kMaxHeight, &max_requested_height);
+      GetMandatoryConstraintValue(constraints, kMaxHeight,
+                                  &max_requested_height);
 
       state_ = RETRIEVING_CAPABILITIES;
       GetCurrentSupportedFormats(max_requested_width,