Reland the CL to remove candidates when doing continual gathering

webrtc/p2p/base/dtlstransportchannel.h

Index: webrtc/p2p/base/dtlstransportchannel.h
diff --git a/webrtc/p2p/base/dtlstransportchannel.h b/webrtc/p2p/base/dtlstransportchannel.h
index ad30441a151f09be87feda07742438d1589572a4..a58b1a0f6b8de695cbe1ce5c5192b50a74f8ccf4 100644
--- a/webrtc/p2p/base/dtlstransportchannel.h
+++ b/webrtc/p2p/base/dtlstransportchannel.h
@@ -186,6 +186,9 @@ class DtlsTransportChannelWrapper : public TransportChannelImpl {
   void AddRemoteCandidate(const Candidate& candidate) override {
     channel_->AddRemoteCandidate(candidate);
   }
+  void RemoveRemoteCandidate(const Candidate& candidate) override {
+    channel_->RemoveRemoteCandidate(candidate);
+  }
 
   void SetIceConfig(const IceConfig& config) override {
     channel_->SetIceConfig(config);
@@ -209,6 +212,8 @@ class DtlsTransportChannelWrapper : public TransportChannelImpl {
   bool HandleDtlsPacket(const char* data, size_t size);
   void OnGatheringState(TransportChannelImpl* channel);
   void OnCandidateGathered(TransportChannelImpl* channel, const Candidate& c);
+  void OnCandidatesRemoved(TransportChannelImpl* channel,
+                           const Candidates& candidates);
   void OnRoleConflict(TransportChannelImpl* channel);
   void OnRouteChange(TransportChannel* channel, const Candidate& candidate);
   void OnConnectionRemoved(TransportChannelImpl* channel);