Bug 1219910 - make gSocketThread a relaxed atomic variable; r=mcmanus

Many places that (re-)declared gSocketThread already included
nsSocketTransportService2.h; we can delete the declaration for those
places.  For all the other places, we need to include
nsSocketTransportService2.h.

netwerk/protocol/websocket/WebSocketChannel.cpp

@@ -55,6 +55,7 @@
 #include "mozilla/StaticMutex.h"
 #include "mozilla/Telemetry.h"
 #include "mozilla/TimeStamp.h"
+#include "nsSocketTransportService2.h"
 
 #include "plbase64.h"
 #include "prmem.h"
@@ -70,8 +71,6 @@
 // dupe one constant we need from it
 #define CLOSE_GOING_AWAY 1001
 
-extern PRThread *gSocketThread;
-
 using namespace mozilla;
 using namespace mozilla::net;