Re-land r9378 "Rename APM Config DelayCorrection to ExtendedFilter"

talk/app/webrtc/mediaconstraintsinterface.h

Index: talk/app/webrtc/mediaconstraintsinterface.h
diff --git a/talk/app/webrtc/mediaconstraintsinterface.h b/talk/app/webrtc/mediaconstraintsinterface.h
index cc682097f76bded91b9106eb63e404181ba6e286..31cc99622f203006c2f4d9b445fc317e4bfa554b 100644
--- a/talk/app/webrtc/mediaconstraintsinterface.h
+++ b/talk/app/webrtc/mediaconstraintsinterface.h
@@ -74,7 +74,10 @@ class MediaConstraintsInterface {
   // Constraint keys used by a local audio source.
   // These keys are google specific.
   static const char kEchoCancellation[];  // googEchoCancellation
+  // TODO(henrik.lundin) Remove kExperimentalEchoCancellation.
+  // https://code.google.com/p/webrtc/issues/detail?id=4696
   static const char kExperimentalEchoCancellation[];  // googEchoCancellation2
+  static const char kExtendedFilterEchoCancellation[];  // googEchoCancellation2
   static const char kDAEchoCancellation[];  // googDAEchoCancellation
   static const char kAutoGainControl[];  // googAutoGainControl
   static const char kExperimentalAutoGainControl[];  // googAutoGainControl2