Fix crash on IP address change.

net/base/host_resolver_impl.cc

Index: net/base/host_resolver_impl.cc
diff --git a/net/base/host_resolver_impl.cc b/net/base/host_resolver_impl.cc
index 1f43c606b2b329115e19ead6a447bcc548525e89..df5bc7905b2f8acb3ef67c8fb5d70a416795fdbc 100644
--- a/net/base/host_resolver_impl.cc
+++ b/net/base/host_resolver_impl.cc
@@ -683,6 +683,8 @@ HostResolverImpl::HostResolverImpl(
 #if defined(OS_WIN)
   EnsureWinsockInit();
 #endif
+  if (network_change_notifier_)
+    network_change_notifier_->AddObserver(this);
 }
 
 HostResolverImpl::~HostResolverImpl() {
@@ -697,6 +699,9 @@ HostResolverImpl::~HostResolverImpl() {
   if (cur_completing_job_)
     cur_completing_job_->Cancel();
 
+  if (network_change_notifier_)
+    network_change_notifier_->RemoveObserver(this);
+
   // Delete the job pools.
   for (size_t i = 0u; i < arraysize(job_pools_); ++i)
     delete job_pools_[i];
@@ -841,7 +846,7 @@ void HostResolverImpl::SetDefaultAddressFamily(AddressFamily address_family) {
 void HostResolverImpl::ProbeIPv6Support() {
   DCHECK(!ipv6_probe_monitoring_);
   ipv6_probe_monitoring_ = true;
-  Flush();  // Give initial setup call.
+  OnIPAddressChanged();  // Give initial setup call.
 }
 
 void HostResolverImpl::Shutdown() {
@@ -1074,7 +1079,7 @@ void HostResolverImpl::OnCancelRequest(const BoundNetLog& net_log,
   net_log.EndEvent(NetLog::TYPE_HOST_RESOLVER_IMPL);
 }
 
-void HostResolverImpl::Flush() {
+void HostResolverImpl::OnIPAddressChanged() {
   if (cache_.get())
     cache_->clear();
   if (ipv6_probe_monitoring_) {