Change HostResolverImplDnsTest.NoIPv6OnWifi to no longer leak

net/dns/host_resolver_impl_unittest.cc

Index: net/dns/host_resolver_impl_unittest.cc
diff --git a/net/dns/host_resolver_impl_unittest.cc b/net/dns/host_resolver_impl_unittest.cc
index 4a963be528e2514707b8edce1c206a284433c17f..0869910bee28ea58c92dff4bf8dcd4f2a652efb1 100644
--- a/net/dns/host_resolver_impl_unittest.cc
+++ b/net/dns/host_resolver_impl_unittest.cc
@@ -2407,14 +2407,12 @@ TEST_F(HostResolverImplDnsTest, ManuallyDisableDnsClientWithPendingRequests) {
   EXPECT_TRUE(requests_[2]->HasOneAddress("192.168.0.3", 80));
 }
 
-// TODO(crbug.com/728808): This test causes HttpNetworkTransactionTests to crash
-// on iOS.
-#if defined(OS_IOS)
-#define MAYBE_NoIPv6OnWifi DISABLED_NoIPv6OnWifi
-#else
-#define MAYBE_NoIPv6OnWifi NoIPv6OnWifi
-#endif
-TEST_F(HostResolverImplDnsTest, MAYBE_NoIPv6OnWifi) {
+TEST_F(HostResolverImplDnsTest, NoIPv6OnWifi) {
+  // CreateSerialResolver will destroy the current resolver_ which will attempt
+  // to remove itself from the NetworkChangeNotifier. If this happens after a
+  // new NetworkChangeNotifier is active, then it will not remove itself from
+  // the old NetworkChangeNotifier which is a potential use-after-free.
+  resolver_ = nullptr;
   test::ScopedMockNetworkChangeNotifier notifier;
   CreateSerialResolver();  // To guarantee order of resolutions.
   resolver_->SetNoIPv6OnWifi(true);