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

net/disk_cache/blockfile/backend_impl_v3.cc

Index: net/disk_cache/blockfile/backend_impl_v3.cc
diff --git a/net/disk_cache/blockfile/backend_impl_v3.cc b/net/disk_cache/blockfile/backend_impl_v3.cc
index 961575510e5f85e9bbedb0e6557f2c897b0238c8..64016c413715d36dc534363972ab977e70f768d5 100644
--- a/net/disk_cache/blockfile/backend_impl_v3.cc
+++ b/net/disk_cache/blockfile/backend_impl_v3.cc
@@ -667,8 +667,8 @@ class BackendImplV3::IteratorImpl : public Backend::Iterator {
       : background_queue_(background_queue), data_(NULL) {
   }
 
-  virtual int OpenNextEntry(Entry** next_entry,
-                            const net::CompletionCallback& callback) override {
+  int OpenNextEntry(Entry** next_entry,
+                    const net::CompletionCallback& callback) override {
     if (!background_queue_)
       return net::ERR_FAILED;
     background_queue_->OpenNextEntry(&data_, next_entry, callback);