net: Fix more clang warnings about missing virtual and OVERRIDE annotations.

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 929cefeed96c209e789ab7b0fe19cc7af594877e..7decae83d91aefc034e69ca75935ffde6e45254d 100644
--- a/net/proxy/proxy_service.cc
+++ b/net/proxy/proxy_service.cc
@@ -373,9 +373,10 @@ class UnsetProxyConfigService : public ProxyConfigService {
   UnsetProxyConfigService() {}
   virtual ~UnsetProxyConfigService() {}
 
-  virtual void AddObserver(Observer* observer) {}
-  virtual void RemoveObserver(Observer* observer) {}
-  virtual ConfigAvailability GetLatestProxyConfig(ProxyConfig* config) {
+  virtual void AddObserver(Observer* observer) OVERRIDE {}
+  virtual void RemoveObserver(Observer* observer) OVERRIDE {}
+  virtual ConfigAvailability GetLatestProxyConfig(
+      ProxyConfig* config) OVERRIDE {
     return CONFIG_UNSET;
   }
 };