Remove global list of SRTP sessions.

talk/session/media/srtpfilter.h

Index: talk/session/media/srtpfilter.h
diff --git a/talk/session/media/srtpfilter.h b/talk/session/media/srtpfilter.h
index 3c3a8e848b2b9db52b59778c8975d28e25549017..fb52222d2181ac670f3d0026aade4871051cc968 100644
--- a/talk/session/media/srtpfilter.h
+++ b/talk/session/media/srtpfilter.h
@@ -40,6 +40,7 @@
 #include "webrtc/base/scoped_ptr.h"
 #include "webrtc/base/sigslotrepeater.h"
 #include "webrtc/base/sslstreamadapter.h"
+#include "webrtc/base/thread_checker.h"
 
 // Forward declaration to avoid pulling in libsrtp headers here
 struct srtp_event_data_t;
@@ -240,8 +241,7 @@ 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_;