Allow to negotiate dependency descriptor rtp header extension

Without exposing it in capabilities:
this extension is not stable enough to expose it by default,
but already in working state so with munge sdp can be experimented with.

Bug: webrtc:10342
Change-Id: I6bac123325a90431e4769e86da79638869e36cfc
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/168961
Reviewed-by: Magnus Flodman <mflodman@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30645}

pc/media_session.cc

@@ -1074,9 +1074,12 @@ static void NegotiateRtpHeaderExtensions(
           webrtc::RtpExtension::kTransportSequenceNumberV2Uri);
 
   bool frame_descriptor_in_local = false;
+  bool dependency_descriptor_in_local = false;
   for (const webrtc::RtpExtension& ours : local_extensions) {
     if (ours.uri == webrtc::RtpExtension::kGenericFrameDescriptorUri00)
       frame_descriptor_in_local = true;
+    else if (ours.uri == webrtc::RtpExtension::kDependencyDescriptorUri)
+      dependency_descriptor_in_local = true;
     webrtc::RtpExtension theirs;
     if (FindByUriWithEncryptionPreference(
             offered_extensions, ours.uri,
@@ -1100,14 +1103,20 @@ static void NegotiateRtpHeaderExtensions(
     negotiated_extensions->push_back(*transport_sequence_number_v2_offer);
   }
 
-  // Frame descriptor support. If the extension is not present locally, but is
+  // Frame descriptors support. If the extension is not present locally, but is
   // in the offer, we add it to the list.
-  if (!frame_descriptor_in_local) {
   webrtc::RtpExtension theirs;
-    if (FindByUriWithEncryptionPreference(
+  if (!dependency_descriptor_in_local &&
+      FindByUriWithEncryptionPreference(
+          offered_extensions, webrtc::RtpExtension::kDependencyDescriptorUri,
+          enable_encrypted_rtp_header_extensions, &theirs)) {
+    negotiated_extensions->push_back(theirs);
+  }
+  if (!frame_descriptor_in_local &&
+      FindByUriWithEncryptionPreference(
           offered_extensions,
           webrtc::RtpExtension::kGenericFrameDescriptorUri00,
-            enable_encrypted_rtp_header_extensions, &theirs))
+          enable_encrypted_rtp_header_extensions, &theirs)) {
     negotiated_extensions->push_back(theirs);
   }
 }

pc/media_session_unittest.cc

@@ -88,6 +88,7 @@ using rtc::CS_AES_CM_128_HMAC_SHA1_80;
 using rtc::UniqueRandomIdGenerator;
 using ::testing::Contains;
 using ::testing::Each;
+using ::testing::ElementsAre;
 using ::testing::ElementsAreArray;
 using ::testing::Eq;
 using ::testing::Field;
@@ -1721,6 +1722,40 @@ TEST_F(MediaSessionDescriptionFactoryTest,
       ElementsAreArray(offered));
 }
 
+TEST_F(MediaSessionDescriptionFactoryTest,
+       NegotiateDependencyDescriptorWhenUnexposedLocally) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  RtpExtension offer_dd(RtpExtension::kDependencyDescriptorUri, 7);
+  RtpExtension local_tsn(RtpExtension::kTransportSequenceNumberUri, 5);
+  f1_.set_video_rtp_header_extensions({offer_dd});
+  f2_.set_video_rtp_header_extensions({local_tsn});
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+  EXPECT_THAT(
+      GetFirstVideoContentDescription(answer.get())->rtp_header_extensions(),
+      ElementsAre(offer_dd));
+}
+
+TEST_F(MediaSessionDescriptionFactoryTest,
+       NegotiateDependencyDescriptorWhenExposedLocally) {
+  MediaSessionOptions opts;
+  AddAudioVideoSections(RtpTransceiverDirection::kRecvOnly, &opts);
+
+  RtpExtension offer_dd(RtpExtension::kDependencyDescriptorUri, 7);
+  RtpExtension local_dd(RtpExtension::kDependencyDescriptorUri, 5);
+  f1_.set_video_rtp_header_extensions({offer_dd});
+  f2_.set_video_rtp_header_extensions({local_dd});
+  std::unique_ptr<SessionDescription> offer = f1_.CreateOffer(opts, nullptr);
+  std::unique_ptr<SessionDescription> answer =
+      f2_.CreateAnswer(offer.get(), opts, nullptr);
+  EXPECT_THAT(
+      GetFirstVideoContentDescription(answer.get())->rtp_header_extensions(),
+      ElementsAre(offer_dd));
+}
+
 TEST_F(MediaSessionDescriptionFactoryTest,
        TestOfferAnswerWithEncryptedRtpExtensionsBoth) {
   MediaSessionOptions opts;