Adds a WebRTC browser_test with opus dtx enabled.

chrome/test/data/webrtc/munge_sdp.js

 /**
  * Copyright 2016 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.
  */
 
 /**
  * See |setSdpDefaultCodec|.
  */
 function setSdpDefaultAudioCodec(sdp, codec) {
   return setSdpDefaultCodec(sdp, 'audio', codec);
 }
 
 /**
  * See |setSdpDefaultCodec|.
  */
 function setSdpDefaultVideoCodec(sdp, codec) {
   return setSdpDefaultCodec(sdp, 'video', codec);
 }
 
 /**
+ * Returns a modified version of |sdp| where the opus DTX flag has been
+ * enabled.
+ */
+function setOpusDtxEnabled(sdp) {
+  var sdpLines = splitSdpLines(sdp);
+
+  // Get default audio codec
+  var defaultCodec = getSdpDefaultAudioCodec(sdp);
+  if (defaultCodec !== 'opus') {
+    failure('setOpusDtxEnabled',
+             'Default audio codec is not set to \'opus\'.');
+  }
+
+  // Find codec ID for Opus, e.g. 111 if 'a=rtpmap:111 opus/48000/2'.
+  var codecId = findRtpmapId(sdpLines, 'opus');
+  if (codecId === null) {
+    failure('setOpusDtxEnabled', 'Unknown ID for |codec| = \'opus\'.');
+  }
+
+  // Find 'a=fmtp:111' line, where 111 is the codecId
+  var fmtLineNo = findLine(sdpLines, 'a=fmtp:' + codecId);
+  if (fmtLineNo === null) {
+    failure('setOpusDtxEnabled',
+             '\'a=fmtp:' + codecId + '\' line missing from |sdp|.');
+  }
+
+  // Modify the line to enable Opus Dtx.
+  sdpLines[fmtLineNo] += ';usedtx=1'
+  return mergeSdpLines(sdpLines);
+}
+
+/**
+ * Check if the opus Dtx flag has been set in |sdp|.
+ */
+function checkOpusDtxEnabled(sdp) {
+  var defaultAudioCodec = getSdpDefaultAudioCodec(sdp);
+  if (defaultAudioCodec !== 'opus') {
+    failure('verifyOpusDtxEnabled',
+             'Default audio codec is not set to opus.');
+  }
+  var sdpLines = splitSdpLines(sdp);
+  // Find codec ID for Opus, e.g. 111 if 'a=rtpmap:111 opus/48000/2'.
+  var codecId = findRtpmapId(sdpLines, 'opus');
+  if (codecId === null) {
+    failure('verifyOpusDtxEnabled', 'Unknown ID for |codec| = \'opus\'.');
+  }
+
+  // Find 'a=fmtp:111' line, where 111 is the codecId
+  var fmtLineNo = findLine(sdpLines, 'a=fmtp:' + codecId);
+  if (fmtLineNo === null) {
+    failure('verifyOpusDtxEnabled',
+             '\'a=fmtp:' + codecId + '\' line missing from |sdp|.');
+  }
+
+  // Check that 'usedtx=1' appears on the line.
+  if (sdpLines[fmtLineNo].indexOf('usedtx=1') === -1) {
+    failure('verifyOpusDtxEnabled',
+             '\'usedtx=1\' is missing from \'a=fmtp:' + codecId + '\' line.');
+  }
+}
+
+/**
  * Returns a modified version of |sdp| where the |codec| has been promoted to be
  * the default codec, i.e. the codec whose ID is first in the list of codecs on
  * the 'm=|type|' line, where |type| is 'audio' or 'video'.
  * @private
  */
 function setSdpDefaultCodec(sdp, type, codec) {
   var sdpLines = splitSdpLines(sdp);
 
   // Find codec ID, e.g. 100 for 'VP8' if 'a=rtpmap:100 VP8/9000'.
   var codecId = findRtpmapId(sdpLines, codec);
@@ skipping 168 matching lines @@
 }
 
 /** @private */
 function findLine(lines, startsWith) {
   for (var i = 0; i < lines.length; i++) {
     if (lines[i].startsWith(startsWith))
       return i;
   }
   return null;
 }