Update some comments/nits following r7486.

chrome/common/json_value_serializer.cc

 // Copyright (c) 2006-2008 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.
 
 #include "chrome/common/json_value_serializer.h"
 
 #include "base/file_util.h"
 #include "base/json_reader.h"
 #include "base/json_writer.h"
 #include "base/string_util.h"
 #include "chrome/common/logging_chrome.h"
 
 JSONStringValueSerializer::~JSONStringValueSerializer() {}
 
 bool JSONStringValueSerializer::Serialize(const Value& root) {
   if (!json_string_ || initialized_with_const_string_)
     return false;
 
   JSONWriter::Write(&root, pretty_print_, json_string_);
 
   return true;
 }
 
 Value* JSONStringValueSerializer::Deserialize(std::string* error_message) {
   if (!json_string_)
-    return false;
+    return NULL;
 
   return JSONReader::ReadAndReturnError(*json_string_, allow_trailing_comma_,
                                         error_message);
 }
 
 /******* File Serializer *******/
 
 bool JSONFileValueSerializer::Serialize(const Value& root) {
   std::string json_string;
   JSONStringValueSerializer serializer(&json_string);
   serializer.set_pretty_print(true);
   bool result = serializer.Serialize(root);
   if (!result)
     return false;
 
   int data_size = static_cast<int>(json_string.size());
   if (file_util::WriteFile(json_file_path_,
                            json_string.data(),
                            data_size) != data_size)
     return false;
 
   return true;
 }
 
 Value* JSONFileValueSerializer::Deserialize(std::string* error_message) {
   std::string json_string;
   if (!file_util::ReadFileToString(json_file_path_, &json_string)) {
-    return false;
+    return NULL;
   }
   JSONStringValueSerializer serializer(json_string);
   return serializer.Deserialize(error_message);
 }