Bug 1513542 - We need to use gAllURLsMutex before destructor of a static variable. r=valentin

Differential Revision: https://phabricator.services.mozilla.com/D16847

--HG--
extra : moz-landing-system : lando

netwerk/base/nsStandardURL.cpp

@@ -286,6 +286,7 @@ void nsStandardURL::ShutdownGlobalObjects() {
     // This instanciates a dummy class, and will trigger the class
     // destructor when libxul is unloaded. This is equivalent to atexit(),
     // but gracefully handles dlclose().
+    StaticMutexAutoLock lock(gAllURLsMutex);
     static DumpLeakedURLs d;
   }
 #endif