Remove candidates when doing continual gathering

webrtc/api/jsepsessiondescription.h

Index: webrtc/api/jsepsessiondescription.h
diff --git a/webrtc/api/jsepsessiondescription.h b/webrtc/api/jsepsessiondescription.h
index 244ee1921277656b64e9361f7f1db1bd87964b13..d27f8a018bb222c2de4c4378fcf2d2a1b15c16cd 100644
--- a/webrtc/api/jsepsessiondescription.h
+++ b/webrtc/api/jsepsessiondescription.h
@@ -57,6 +57,8 @@ class JsepSessionDescription : public SessionDescriptionInterface {
   // Allow changing the type. Used for testing.
   void set_type(const std::string& type) { type_ = type; }
   virtual bool AddCandidate(const IceCandidateInterface* candidate);
+  virtual int RemoveCandidates(
+      const std::vector<IceCandidateInterfaceRefPtr>& candidates);
   virtual size_t number_of_mediasections() const;
   virtual const IceCandidateCollection* candidates(
       size_t mediasection_index) const;
@@ -72,6 +74,8 @@ class JsepSessionDescription : public SessionDescriptionInterface {
   static const int kDefaultVideoCodecPreference;
 
  private:
+  int RemoveCandidate(const IceCandidateInterface* candidate);
+
   rtc::scoped_ptr<cricket::SessionDescription> description_;
   std::string session_id_;
   std::string session_version_;