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

net/disk_cache/blockfile/sparse_control_v3.cc

Index: net/disk_cache/blockfile/sparse_control_v3.cc
diff --git a/net/disk_cache/blockfile/sparse_control_v3.cc b/net/disk_cache/blockfile/sparse_control_v3.cc
index cba0ed5393f180e17dce388c900119f8df22ccb5..fa6829f0e475e7a29d1cc7f5e8490f5f34da9bc8 100644
--- a/net/disk_cache/blockfile/sparse_control_v3.cc
+++ b/net/disk_cache/blockfile/sparse_control_v3.cc
@@ -56,7 +56,7 @@ class ChildrenDeleter
   ChildrenDeleter(disk_cache::BackendImpl* backend, const std::string& name)
       : backend_(backend->GetWeakPtr()), name_(name), signature_(0) {}
 
-  virtual void OnFileIOComplete(int bytes_copied) override;
+  void OnFileIOComplete(int bytes_copied) override;
 
   // Two ways of deleting the children: if we have the children map, use Start()
   // directly, otherwise pass the data address to ReadData().
@@ -65,7 +65,7 @@ class ChildrenDeleter
 
  private:
   friend class base::RefCounted<ChildrenDeleter>;
-  virtual ~ChildrenDeleter() {}
+  ~ChildrenDeleter() override {}
 
   void DeleteChildren();