Reland "Expose can_trickle_ice_candidates on PeerConnection"

This reverts commit cb8c40138ca170f841bc45fa6771cdfc4b966e5f.

Reason for revert: Added missing default.

Original change's description:
> Revert "Expose can_trickle_ice_candidates on PeerConnection"
>
> This reverts commit c6a65c8866487c6adc0a7bb472d3bad9389501f9.
>
> Reason for revert: Breaks downstream due to missing default
>
> Original change's description:
> > Expose can_trickle_ice_candidates on PeerConnection
> >
> > Bug: chromium:708484
> > Change-Id: I9a40e75066341f0d9f965bd3718bfcb3f0459533
> > Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/169450
> > Commit-Queue: Harald Alvestrand <hta@webrtc.org>
> > Reviewed-by: Taylor <deadbeef@webrtc.org>
> > Cr-Commit-Position: refs/heads/master@{#30653}
>
> TBR=deadbeef@webrtc.org,hta@webrtc.org
>
> Change-Id: Iaa5b977c4237715a8a5127cf167cf6512a3f7059
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: chromium:708484
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/169540
> Reviewed-by: Harald Alvestrand <hta@webrtc.org>
> Commit-Queue: Harald Alvestrand <hta@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#30655}

TBR=deadbeef@webrtc.org,hta@webrtc.org

Change-Id: I608da7781f158b4b02dd226d4dcd5615c4935fa8
Bug: chromium:708484
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/169541
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30656}

api/BUILD.gn

@@ -1010,6 +1010,7 @@ if (rtc_include_tests) {
     sources = [ "test/compile_all_headers.cc" ]
 
     deps = [
+      ":dummy_peer_connection",
       ":fake_frame_decryptor",
       ":fake_frame_encryptor",
       ":fake_media_transport",

api/peer_connection_interface.h

@@ -1109,6 +1109,13 @@ class RTC_EXPORT PeerConnectionInterface : public rtc::RefCountInterface {
 
   virtual IceGatheringState ice_gathering_state() = 0;
 
+  // Returns the current state of canTrickleIceCandidates per
+  // https://w3c.github.io/webrtc-pc/#attributes-1
+  virtual absl::optional<bool> can_trickle_ice_candidates() {
+    // TODO(crbug.com/708484): Remove default implementation.
+    return absl::nullopt;
+  }
+
   // Start RtcEventLog using an existing output-sink. Takes ownership of
   // |output| and passes it on to Call, which will take the ownership. If the
   // operation fails the output will be closed and deallocated. The event log

api/peer_connection_proxy.h

@@ -131,6 +131,7 @@ PROXY_METHOD0(IceConnectionState, ice_connection_state)
 PROXY_METHOD0(IceConnectionState, standardized_ice_connection_state)
 PROXY_METHOD0(PeerConnectionState, peer_connection_state)
 PROXY_METHOD0(IceGatheringState, ice_gathering_state)
+PROXY_METHOD0(absl::optional<bool>, can_trickle_ice_candidates)
 PROXY_METHOD2(bool,
               StartRtcEventLog,
               std::unique_ptr<RtcEventLogOutput>,

api/test/dummy_peer_connection.h

@@ -229,6 +229,8 @@ class DummyPeerConnection : public PeerConnectionInterface {
     return IceGatheringState();
   }
 
+  absl::optional<bool> can_trickle_ice_candidates() { return absl::nullopt; }
+
   bool StartRtcEventLog(std::unique_ptr<RtcEventLogOutput> output,
                         int64_t output_period_ms) override {
     return false;

api/test/mock_peerconnectioninterface.h

@@ -127,6 +127,7 @@ class MockPeerConnectionInterface
   MOCK_METHOD0(standardized_ice_connection_state, IceConnectionState());
   MOCK_METHOD0(peer_connection_state, PeerConnectionState());
   MOCK_METHOD0(ice_gathering_state, IceGatheringState());
+  MOCK_METHOD0(can_trickle_ice_candidates, absl::optional<bool>());
   MOCK_METHOD2(StartRtcEventLog,
                bool(std::unique_ptr<RtcEventLogOutput>, int64_t));
   MOCK_METHOD1(StartRtcEventLog, bool(std::unique_ptr<RtcEventLogOutput>));

pc/peer_connection.cc

@@ -2144,6 +2144,23 @@ PeerConnection::ice_gathering_state() {
   return ice_gathering_state_;
 }
 
+absl::optional<bool> PeerConnection::can_trickle_ice_candidates() {
+  RTC_DCHECK_RUN_ON(signaling_thread());
+  SessionDescriptionInterface* description = current_remote_description_.get();
+  if (!description) {
+    description = pending_remote_description_.get();
+  }
+  if (!description) {
+    return absl::nullopt;
+  }
+  // TODO(bugs.webrtc.org/7443): Change to retrieve from session-level option.
+  if (description->description()->transport_infos().size() < 1) {
+    return absl::nullopt;
+  }
+  return description->description()->transport_infos()[0].description.HasOption(
+      "trickle");
+}
+
 rtc::scoped_refptr<DataChannelInterface> PeerConnection::CreateDataChannel(
     const std::string& label,
     const DataChannelInit* config) {

pc/peer_connection.h

@@ -189,6 +189,7 @@ class PeerConnection : public PeerConnectionInternal,
   IceConnectionState standardized_ice_connection_state() override;
   PeerConnectionState peer_connection_state() override;
   IceGatheringState ice_gathering_state() override;
+  absl::optional<bool> can_trickle_ice_candidates() override;
 
   const SessionDescriptionInterface* local_description() const override;
   const SessionDescriptionInterface* remote_description() const override;

pc/peer_connection_interface_unittest.cc

@@ -3485,7 +3485,10 @@ TEST_P(PeerConnectionInterfaceTest, OffersAndAnswersHaveTrickleIceOption) {
   EXPECT_TRUE(desc->transport_infos()[1].description.HasOption("trickle"));
 
   // Apply the offer as a remote description, then create an answer.
+  EXPECT_FALSE(pc_->can_trickle_ice_candidates());
   EXPECT_TRUE(DoSetRemoteDescription(std::move(offer)));
+  ASSERT_TRUE(pc_->can_trickle_ice_candidates());
+  EXPECT_TRUE(*(pc_->can_trickle_ice_candidates()));
   std::unique_ptr<SessionDescriptionInterface> answer;
   ASSERT_TRUE(DoCreateAnswer(&answer, &options));
   desc = answer->description();

pc/test/fake_peer_connection_base.h

@@ -217,6 +217,8 @@ class FakePeerConnectionBase : public PeerConnectionInternal {
     return IceGatheringState::kIceGatheringNew;
   }
 
+  absl::optional<bool> can_trickle_ice_candidates() { return absl::nullopt; }
+
   bool StartRtcEventLog(std::unique_ptr<RtcEventLogOutput> output,
                         int64_t output_period_ms) override {
     return false;