Definition
WebRTC: Real-Time Communication in Browsers defines RTCIceCandidateType
enum RTCIceCandidateType {
  "host",
  "srflx",
  "prflx",
  "relay"
};
  
  
Referring IDL interfaces/dictionaries
Referring specifications
- Identifiers for WebRTC's Statistics API refers to 
RTCIceCandidateType