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

base/prefs/pref_member.h

Index: base/prefs/pref_member.h
diff --git a/base/prefs/pref_member.h b/base/prefs/pref_member.h
index 078be951b47c68ac15f81105febd7a85975824cc..9b140d16748e7ea5516687ea9ab9b514452c1c84 100644
--- a/base/prefs/pref_member.h
+++ b/base/prefs/pref_member.h
@@ -264,9 +264,9 @@ class PrefMember : public subtle::PrefMemberBase {
     }
 
    protected:
-    virtual ~Internal() {}
+    ~Internal() override {}
 
-    virtual BASE_PREFS_EXPORT bool UpdateValueInternal(
+    BASE_PREFS_EXPORT bool UpdateValueInternal(
         const base::Value& value) const override;
 
     // We cache the value of the pref so we don't have to keep walking the pref
@@ -277,8 +277,8 @@ class PrefMember : public subtle::PrefMemberBase {
     DISALLOW_COPY_AND_ASSIGN(Internal);
   };
 
-  virtual Internal* internal() const override { return internal_.get(); }
-  virtual void CreateInternal() const override { internal_ = new Internal(); }
+  Internal* internal() const override { return internal_.get(); }
+  void CreateInternal() const override { internal_ = new Internal(); }
 
   // This method is used to do the actual sync with pref of the specified type.
   void BASE_PREFS_EXPORT UpdatePref(const ValueType& value);