Reland the CL to remove candidates when doing continual gathering

webrtc/api/jsepicecandidate.h

Index: webrtc/api/jsepicecandidate.h
diff --git a/webrtc/api/jsepicecandidate.h b/webrtc/api/jsepicecandidate.h
index 529b2a7756de8ea0ebf33e714fb6e63eb04176a6..7e9500bceac59806d98cb2a62cbe5b084b2869ec 100644
--- a/webrtc/api/jsepicecandidate.h
+++ b/webrtc/api/jsepicecandidate.h
@@ -70,6 +70,9 @@ class JsepCandidateCollection : public IceCandidateCollection {
   virtual const IceCandidateInterface* at(size_t index) const {
     return candidates_[index];
   }
+  // Removes the candidate that has a matching address and protocol.
+  // Returns the number of candidates that were removed.
+  size_t remove(const cricket::Candidate& candidate);
 
  private:
   std::vector<JsepIceCandidate*> candidates_;