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

base/prefs/pref_member.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // A helper class that stays in sync with a preference (bool, int, real,
 // string or filepath).  For example:
 //
 // class MyClass {
 //  public:
 //   MyClass(PrefService* prefs) {
@@ skipping 246 matching lines @@
   class Internal : public subtle::PrefMemberBase::Internal {
    public:
     Internal() : value_(ValueType()) {}
 
     ValueType value() {
       CheckOnCorrectThread();
       return value_;
     }
 
    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
     // tree.
     mutable ValueType value_;
 
    private:
     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);
 
   mutable scoped_refptr<Internal> internal_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefMember);
 };
 
 // Declaration of template specialization need to be repeated here
@@ skipping 57 matching lines @@
 
 typedef PrefMember<bool> BooleanPrefMember;
 typedef PrefMember<int> IntegerPrefMember;
 typedef PrefMember<double> DoublePrefMember;
 typedef PrefMember<std::string> StringPrefMember;
 typedef PrefMember<base::FilePath> FilePathPrefMember;
 // This preference member is expensive for large string arrays.
 typedef PrefMember<std::vector<std::string> > StringListPrefMember;
 
 #endif  // BASE_PREFS_PREF_MEMBER_H_