Add error messages to JSONReader and friends. This required a bit of refactor...

chrome/common/json_value_serializer.h

 // 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.
 
 #ifndef CHROME_COMMON_JSON_VALUE_SERIALIZER_H__
 #define CHROME_COMMON_JSON_VALUE_SERIALIZER_H__
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 23 matching lines @@
 
   // 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);
 
   // 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 true, the |root| parameter will be set to point to a new Value
   // object that corresponds to the values represented in the string.  The
-  // caller takes ownership of the returned Value objects.
-  bool Deserialize(Value** root);
+  // caller takes ownership of the returned Value objects. Otherwise, the root
+  // value will be changed and if |error_message| is non-null, it will contain
+  // a string describing the error.
+  bool Deserialize(Value** root, 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_;
@@ skipping 23 matching lines @@
   //
   // 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);
 
   // 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 true, the |root| parameter will be set to point to a new Value
   // object that corresponds to the values represented in the file.  The
-  // caller takes ownership of the returned Value objects.
-  bool Deserialize(Value** root);
+  // caller takes ownership of the returned Value objects. Otherwise, the root
+  // value will be changed and if |error_message| is non-null, it will contain
+  // a string describing the error.
+  bool Deserialize(Value** root, std::string* error_message);
 
  private:
   std::wstring json_file_path_;
 
   DISALLOW_EVIL_CONSTRUCTORS(JSONFileValueSerializer);
 };
 
 #endif  // CHROME_COMMON_JSON_VALUE_SERIALIZER_H__