Add the "virtual" keyword on method overrides that are missing it.

chrome/common/json_value_serializer.h

 // Copyright (c) 2009 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.
 
 #ifndef CHROME_COMMON_JSON_VALUE_SERIALIZER_H_
 #define CHROME_COMMON_JSON_VALUE_SERIALIZER_H_
 #pragma once
 
 #include <string>
 
@@ skipping 15 matching lines @@
 
   // This version allows initialization with a const string reference for
   // deserialization only.
   explicit JSONStringValueSerializer(const std::string& json_string)
       : json_string_(&const_cast<std::string&>(json_string)),
         initialized_with_const_string_(true),
         pretty_print_(false),
         allow_trailing_comma_(false) {
   }
 
-  ~JSONStringValueSerializer();
+  virtual ~JSONStringValueSerializer();
 
   // Attempt to serialize the data structure represented by Value into
   // JSON.  If the return value is true, the result will have been written
   // into the string passed into the constructor.
-  bool Serialize(const Value& root);
+  virtual bool Serialize(const Value& root);
 
   // Attempt to deserialize the data structure encoded in the string passed
   // in to the constructor into a structure of Value objects.  If the return
   // value is NULL, and if |error_code| is non-null, |error_code| will
   // contain an integer error code (either JsonFileError or JsonParseError).
   // If |error_message| is non-null, it will be filled in with a formatted
   // error message including the location of the error if appropriate.
   // The caller takes ownership of the returned value.
-  Value* Deserialize(int* error_code, std::string* error_message);
+  virtual Value* Deserialize(int* error_code, std::string* error_message);
 
   void set_pretty_print(bool new_value) { pretty_print_ = new_value; }
   bool pretty_print() { return pretty_print_; }
 
   void set_allow_trailing_comma(bool new_value) {
     allow_trailing_comma_ = new_value;
   }
 
  private:
   std::string* json_string_;
   bool initialized_with_const_string_;
   bool pretty_print_;  // If true, serialization will span multiple lines.
   // If true, deserialization will allow trailing commas.
   bool allow_trailing_comma_;
 
   DISALLOW_COPY_AND_ASSIGN(JSONStringValueSerializer);
 };
 
 class JSONFileValueSerializer : public ValueSerializer {
  public:
   // json_file_patch is the path of a file that will be source of the
   // deserialization or the destination of the serialization.
   // When deserializing, the file should exist, but when serializing, the
   // serializer will attempt to create the file at the specified location.
   explicit JSONFileValueSerializer(const FilePath& json_file_path)
     : json_file_path_(json_file_path) {}
 
-  ~JSONFileValueSerializer() {}
+  virtual ~JSONFileValueSerializer() {}
 
   // DO NOT USE except in unit tests to verify the file was written properly.
   // We should never serialize directly to a file since this will block the
   // thread. Instead, serialize to a string and write to the file you want on
   // the file thread.
   //
   // Attempt to serialize the data structure represented by Value into
   // JSON.  If the return value is true, the result will have been written
   // into the file whose name was passed into the constructor.
-  bool Serialize(const Value& root);
+  virtual bool Serialize(const Value& root);
 
   // Attempt to deserialize the data structure encoded in the file passed
   // in to the constructor into a structure of Value objects.  If the return
   // value is NULL, and if |error_code| is non-null, |error_code| will
   // contain an integer error code (either JsonFileError or JsonParseError).
   // If |error_message| is non-null, it will be filled in with a formatted
   // error message including the location of the error if appropriate.
   // The caller takes ownership of the returned value.
-  Value* Deserialize(int* error_code, std::string* error_message);
+  virtual Value* Deserialize(int* error_code, std::string* error_message);
 
   // This enum is designed to safely overlap with JSONReader::JsonParseError.
   enum JsonFileError {
     JSON_NO_ERROR = 0,
     JSON_ACCESS_DENIED = 1000,
     JSON_CANNOT_READ_FILE,
     JSON_FILE_LOCKED,
     JSON_NO_SUCH_FILE
   };
 
@@ skipping 11 matching lines @@
   FilePath json_file_path_;
 
   // A wrapper for file_util::ReadFileToString which returns a non-zero
   // JsonFileError if there were file errors.
   int ReadFileToString(std::string* json_string);
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSONFileValueSerializer);
 };
 
 #endif  // CHROME_COMMON_JSON_VALUE_SERIALIZER_H_