Fix crash on IP address change.

net/base/host_resolver_impl.h

Index: net/base/host_resolver_impl.h
diff --git a/net/base/host_resolver_impl.h b/net/base/host_resolver_impl.h
index 4814921fc24120b74715d6a6da878fddbc61e860..1a182b36b0b271862bd22e2c5a8fd699acafc81a 100644
--- a/net/base/host_resolver_impl.h
+++ b/net/base/host_resolver_impl.h
@@ -47,7 +47,8 @@ namespace net {
 //
 // Requests are ordered in the queue based on their priority.
 
-class HostResolverImpl : public HostResolver {
+class HostResolverImpl : public HostResolver,
+                         public NetworkChangeNotifier::Observer {
  public:
   // The index into |job_pools_| for the various job pools. Pools with a higher
   // index have lower priority.
@@ -87,7 +88,6 @@ class HostResolverImpl : public HostResolver {
   virtual void CancelRequest(RequestHandle req);
   virtual void AddObserver(HostResolver::Observer* observer);
   virtual void RemoveObserver(HostResolver::Observer* observer);
-  virtual void Flush();
 
   // Set address family, and disable IPv6 probe support.
   virtual void SetDefaultAddressFamily(AddressFamily address_family);
@@ -180,6 +180,9 @@ class HostResolverImpl : public HostResolver {
                        int request_id,
                        const RequestInfo& info);
 
+  // NetworkChangeNotifier::Observer methods:
+  virtual void OnIPAddressChanged();
+
   // Notify IPv6ProbeJob not to call back, and discard reference to the job.
   void DiscardIPv6ProbeJob();