Reland: Remove global list of SRTP sessions.

webrtc/pc/srtpfilter.h

Index: webrtc/pc/srtpfilter.h
diff --git a/webrtc/pc/srtpfilter.h b/webrtc/pc/srtpfilter.h
index b54eb8bc8667d704aadb39764e879fb73e7ec26b..cde9ad7e09c84dbc4a0214cba3505768c3bfcf5b 100644
--- a/webrtc/pc/srtpfilter.h
+++ b/webrtc/pc/srtpfilter.h
@@ -22,6 +22,7 @@
 #include "webrtc/base/criticalsection.h"
 #include "webrtc/base/sigslotrepeater.h"
 #include "webrtc/base/sslstreamadapter.h"
+#include "webrtc/base/thread_checker.h"
 #include "webrtc/media/base/cryptoparams.h"
 #include "webrtc/p2p/base/sessiondescription.h"
 
@@ -225,8 +226,7 @@ class SrtpSession {
   void HandleEvent(const srtp_event_data_t* ev);
   static void HandleEventThunk(srtp_event_data_t* ev);
 
-  static std::list<SrtpSession*>* sessions();
-
+  rtc::ThreadChecker thread_checker_;
   srtp_ctx_t* session_;
   int rtp_auth_tag_len_;
   int rtcp_auth_tag_len_;