Make it possible to keep the port allocator session running

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 6e3efa8c4144d69fdfbb71ba30c6c14c3c09b872..69b5ed0582008806b46a21f8d450cbdf4ab09781 100644
--- a/webrtc/p2p/base/portallocator.h
+++ b/webrtc/p2p/base/portallocator.h
@@ -91,6 +91,9 @@ class PortAllocatorSession : public sigslot::has_slots<> {
   // Starts gathering STUN and Relay configurations.
   virtual void StartGettingPorts() = 0;
   virtual void StopGettingPorts() = 0;
+  // Only stop the existing gathering process but may start new ones if needed.
+  virtual void ClearGettingPorts() = 0;
+  // Whether the process of getting ports has been stopped.
   virtual bool IsGettingPorts() = 0;
 
   sigslot::signal2<PortAllocatorSession*, PortInterface*> SignalPortReady;