message: Add thread annotations to PhysicalSocketServer members
  Cr-Commit-Position: refs/heads/master@{#31301}
diff: #include "rtc_base/net_helpers.h"
  #include "rtc_base/socket_server.h"
  #include "rtc_base/system/rtc_export.h"
  +#include "rtc_base/thread_annotations.h"
  #if defined(WEBRTC_POSIX)
  typedef int SOCKET;
  @@ -82,7 +83,7 @@ class RTC_EXPORT PhysicalSocketServer : public SocketServer {
  private:
  typedef std::set<Dispatcher*> DispatcherSet;
  - void AddRemovePendingDispatchers();
  + void AddRemovePendingDispatchers() RTC_EXCLUSIVE_LOCKS_REQUIRED(crit_);
  #if defined(WEBRTC_POSIX)
  bool WaitSelect(int cms, bool process_io);
  @@ -97,11 +98,11 @@ class RTC_EXPORT PhysicalSocketServer : public SocketServer {
  const int epoll_fd_ = INVALID_SOCKET;
  std::vector<struct epoll_event> epoll_events_;
  #endif // WEBRTC_USE_EPOLL
  - DispatcherSet dispatchers_;
  - DispatcherSet pending_add_dispatchers_;
  - DispatcherSet pending_remove_dispatchers_;
  - bool processing_dispatchers_ = false;
  - Signaler* signal_wakeup_;
  + DispatcherSet dispatchers_ RTC_GUARDED_BY(crit_);
  + DispatcherSet pending_add_dispatchers_ RTC_GUARDED_BY(crit_);
  + DispatcherSet pending_remove_dispatchers_ RTC_GUARDED_BY(crit_);
  + bool processing_dispatchers_ RTC_GUARDED_BY(crit_) = false;
  + Signaler* signal_wakeup_; // Assigned in constructor only
  CriticalSection crit_;
  #if defined(WEBRTC_WIN)
  const WSAEVENT socket_ev_;
  