Adds a WebRTC browser_test with opus dtx enabled.

chrome/test/data/webrtc/peerconnection.js

Index: chrome/test/data/webrtc/peerconnection.js
diff --git a/chrome/test/data/webrtc/peerconnection.js b/chrome/test/data/webrtc/peerconnection.js
index 639e0f41a8ff34624bc5be8ea6fed1aeb640b757..ff5980c1a43741ab78ad61cc9afd08c9f2ce3f40 100644
--- a/chrome/test/data/webrtc/peerconnection.js
+++ b/chrome/test/data/webrtc/peerconnection.js
@@ -77,8 +77,12 @@ function preparePeerConnectionWithCertificate(certificate) {
  *     the default video codec, e.g. the first one in the list on the 'm=video'
  *     SDP offer line. |videoCodec| is the case-sensitive codec name, e.g.
  *     'VP8' or 'H264'.
+ * @param {boolean} enableOpusDtx If true, enable Opus Dtx, e.g. append
+ *     'usedtx=1' to the appropriate 'a=fmtp' line.
  */
-function createLocalOffer(constraints, videoCodec = null) {
+function createLocalOffer(constraints,
+                          videoCodec = null,
+                          enableOpusDtx = false) {
   peerConnection_().createOffer(
       function(localOffer) {
         success('createOffer');
@@ -86,6 +90,8 @@ function createLocalOffer(constraints, videoCodec = null) {
         setLocalDescription(peerConnection, localOffer);
         if (videoCodec !== null)
           localOffer.sdp = setSdpDefaultVideoCodec(localOffer.sdp, videoCodec);
+        if (enableOpusDtx)
+          localOffer.sdp = setOpusDtxEnabled(localOffer.sdp);
 
         returnToTest('ok-' + JSON.stringify(localOffer));
       },
@@ -101,8 +107,12 @@ function createLocalOffer(constraints, videoCodec = null) {
  * @param {!string} sessionDescJson A JSON-encoded session description of type
  *     'offer'.
  * @param {!Object} constraints Any createAnswer constraints.
+ * @param {boolean} enableOpusDtx If true, enable Opus Dtx, e.g. append
+ *     'usedtx=1' to the appropriate 'a=fmtp' line.
  */
-function receiveOfferFromPeer(sessionDescJson, constraints) {
+function receiveOfferFromPeer(sessionDescJson,
+                              constraints,
+                              enableOpusDtx = false) {
   offer = parseJson_(sessionDescJson);
   if (!offer.type)
     failTest('Got invalid session description from peer: ' + sessionDescJson);
@@ -119,6 +129,8 @@ function receiveOfferFromPeer(sessionDescJson, constraints) {
       function(answer) {
         success('createAnswer');
         setLocalDescription(peerConnection, answer);
+        if (enableOpusDtx)
+          answer.sdp = setOpusDtxEnabled(answer.sdp);
         returnToTest('ok-' + JSON.stringify(answer));
       },
       function(error) { failure('createAnswer', error); },
@@ -154,6 +166,22 @@ function verifyDefaultVideoCodec(sessionDescJson, expectedVideoCodec) {
 }
 
 /**
+ * Verifies that Opus Dtx is enabled, e.g. 'usedtx=1' can be found in the
+ * appropriate 'a=fmtp' line. If this is not the case, |failure| occurs.
+ *
+ * @param {!string} sessionDescJson A JSON-encoded session description.
+ */
+function verifyOpusDtxEnabled(sessionDescJson) {
+  var sessionDesc = parseJson_(sessionDescJson);
+  if (!sessionDesc.type) {
+    failure('verifyOpusDtxEnabled',
+             'Invalid session description: ' + sessionDescJson);
+  }
+  checkOpusDtxEnabled(sessionDesc.sdp);
+  returnToTest('ok-verified');
+}
+
+/**
  * Asks this page to accept an answer generated by the peer in response to a
  * previous offer by this page
  *