Bug 1520642 - Cancel dns requests before cleaning up db. r=kershaw

Differential Revision: https://phabricator.services.mozilla.com/D18989

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

netwerk/dns/nsHostResolver.cpp

@@ -778,6 +778,9 @@ void nsHostResolver::Shutdown() {
 
     if (mNumIdleTasks) mIdleTaskCV.NotifyAll();
 
+    for (auto iter = mRecordDB.Iter(); !iter.Done(); iter.Next()) {
+      iter.UserData()->Cancel();
+    }
     // empty host database
     mRecordDB.Clear();
   }
@@ -797,10 +800,6 @@ void nsHostResolver::Shutdown() {
   pendingQLow.clear();
   evictionQ.clear();
 
-  for (auto iter = mRecordDB.Iter(); !iter.Done(); iter.Next()) {
-    iter.UserData()->Cancel();
-  }
-
   // Shutdown the resolver threads, but with a timeout of 20 seconds.
   // If the timeout is exceeded, any stuck threads will be leaked.
   mResolverThreads->ShutdownWithTimeout(20 * 1000);