Correct const accessors in base/values.(h|cc)

base/json/json_value_converter.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.
 
 #ifndef BASE_JSON_JSON_VALUE_CONVERTER_H_
 #define BASE_JSON_JSON_VALUE_CONVERTER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 487 matching lines @@
   }
 
   bool Convert(const base::Value& value, StructType* output) const {
     const DictionaryValue* dictionary_value = NULL;
     if (!value.GetAsDictionary(&dictionary_value))
       return false;
 
     for(size_t i = 0; i < fields_.size(); ++i) {
       const internal::FieldConverterBase<StructType>* field_converter =
           fields_[i];
-      base::Value* field = NULL;
+      const base::Value* field = NULL;
       if (dictionary_value->Get(field_converter->field_path(), &field)) {
         if (!field_converter->ConvertField(*field, output)) {
           DVLOG(1) << "failure at field " << field_converter->field_path();
           return false;
         }
       }
     }
     return true;
   }
 
  private:
   ScopedVector<internal::FieldConverterBase<StructType> > fields_;
 
   DISALLOW_COPY_AND_ASSIGN(JSONValueConverter);
 };
 
 }  // namespace base
 
 #endif  // BASE_JSON_JSON_VALUE_CONVERTER_H_