Use continual gathering to restore backup connections

webrtc/p2p/base/portallocator.h

Index: webrtc/p2p/base/portallocator.h
diff --git a/webrtc/p2p/base/portallocator.h b/webrtc/p2p/base/portallocator.h
index 6a32b9668f882ddc245f4f2af9bc3683ced930a4..f004990f54983a9de9fc15e8680a16a573d06854 100644
--- a/webrtc/p2p/base/portallocator.h
+++ b/webrtc/p2p/base/portallocator.h
@@ -165,6 +165,15 @@ class PortAllocatorSession : public sigslot::has_slots<> {
   virtual void ClearGettingPorts() = 0;
   // Whether the process of getting ports has been stopped.
   virtual bool IsGettingPorts() = 0;
+  // Re-gathers candidates on networks that do not have any connections. More
+  // precisely, a network interface may have more than one IP addresses (e.g.,
+  // IPv4 and IPv6 addresses). Each address subnet will be used to create a
+  // network. Only if all networks of an interface has no connection,
+  // we will start re-gather on all networks of that interface.
+  virtual void RegatherOnFailedNetworks() {}
+  // Re-gathers candidates on all networks.
+  // TODO(honghaiz): Implement this in BasicPortAllocator.
+  virtual void RegatherOnAllNetworks() {}
 
   // Another way of getting the information provided by the signals below.
   //
@@ -175,8 +184,12 @@ class PortAllocatorSession : public sigslot::has_slots<> {
   virtual bool CandidatesAllocationDone() const = 0;
 
   sigslot::signal2<PortAllocatorSession*, PortInterface*> SignalPortReady;
+  sigslot::signal2<PortAllocatorSession*, const std::vector<PortInterface*>&>
+      SignalPortsRemoved;
   sigslot::signal2<PortAllocatorSession*,
                    const std::vector<Candidate>&> SignalCandidatesReady;
+  sigslot::signal2<PortAllocatorSession*, const std::vector<Candidate>&>
+      SignalCandidatesRemoved;
   sigslot::signal1<PortAllocatorSession*> SignalCandidatesAllocationDone;
 
   virtual uint32_t generation() { return generation_; }