[net] Use only DnsConfigService to detect DNS changes in HostResolverImpl

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 8c2579d8705fb71bacdc6683a2b025ba3ebf1037..3c1b5d2b50b98d5e569ecd1095f88866b7ca35b0 100644
--- a/net/base/host_resolver_impl.h
+++ b/net/base/host_resolver_impl.h
@@ -59,7 +59,6 @@ class NET_EXPORT HostResolverImpl
     : public HostResolver,
       NON_EXPORTED_BASE(public base::NonThreadSafe),
       public NetworkChangeNotifier::IPAddressObserver,
-      public NetworkChangeNotifier::DNSObserver,
       public base::SupportsWeakPtr<HostResolverImpl> {
  public:
   // Parameters for ProcTask which resolves hostnames using HostResolveProc.
@@ -219,9 +218,6 @@ class NET_EXPORT HostResolverImpl
   // NetworkChangeNotifier::IPAddressObserver:
   virtual void OnIPAddressChanged() OVERRIDE;
 
-  // NetworkChangeNotifier::DNSObserver:
-  virtual void OnDNSChanged(unsigned detail) OVERRIDE;
-
   // DnsConfigService callback:
   void OnDnsConfigChanged(const DnsConfig& dns_config);