Change minimum DTMF event duration to be 40 milliseconds

webrtc/media/engine/webrtcvoiceengine.cc

Index: webrtc/media/engine/webrtcvoiceengine.cc
diff --git a/webrtc/media/engine/webrtcvoiceengine.cc b/webrtc/media/engine/webrtcvoiceengine.cc
index f96c8e741e04ad94075ad69add97fab351230e01..52386d70a89eeebb88434081219fb4e790abf1a3 100644
--- a/webrtc/media/engine/webrtcvoiceengine.cc
+++ b/webrtc/media/engine/webrtcvoiceengine.cc
@@ -102,7 +102,7 @@ const rtc::DiffServCodePoint kAudioDscpValue = rtc::DSCP_EF;
 // Constants from voice_engine_defines.h.
 const int kMinTelephoneEventCode = 0;           // RFC4733 (Section 2.3.1)
 const int kMaxTelephoneEventCode = 255;
-const int kMinTelephoneEventDuration = 100;
+const int kMinTelephoneEventDuration = 40;

[the sun, 2017/02/14 21:57:35]

Refer to https://w3c.github.io/webrtc-pc/#rtcdtmfsender in the CL description
(+a comment here).

Also, you should update the limits in webrtc/pc/dtmfsender.cc and add the
missing unit tests.

 const int kMaxTelephoneEventDuration = 60000;   // Actual limit is 2^16
 
 const int kMinPayloadType = 0;