Update {virtual,override,final} to follow C++11 style in net, round 2.

net/proxy/proxy_service.cc

Index: net/proxy/proxy_service.cc
diff --git a/net/proxy/proxy_service.cc b/net/proxy/proxy_service.cc
index 9d5a0b0b32072abae04e5695e70f9442e0291bc9..a62732d87327c655b03aaf8fcc1307a5c0c5de5d 100644
--- a/net/proxy/proxy_service.cc
+++ b/net/proxy/proxy_service.cc
@@ -301,12 +301,11 @@ base::Value* NetLogFinishedResolvingProxyCallback(
 class UnsetProxyConfigService : public ProxyConfigService {
  public:
   UnsetProxyConfigService() {}
-  virtual ~UnsetProxyConfigService() {}
+  ~UnsetProxyConfigService() override {}
 
-  virtual void AddObserver(Observer* observer) override {}
-  virtual void RemoveObserver(Observer* observer) override {}
-  virtual ConfigAvailability GetLatestProxyConfig(
-      ProxyConfig* config) override {
+  void AddObserver(Observer* observer) override {}
+  void RemoveObserver(Observer* observer) override {}
+  ConfigAvailability GetLatestProxyConfig(ProxyConfig* config) override {
     return CONFIG_UNSET;
   }
 };