Make the error_string parameter a reference instead of a pointer to enforce

chrome/browser/privacy_blacklist/blacklist_io.cc

 // 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.
 
 #include "chrome/browser/privacy_blacklist/blacklist_io.h"
 
 #include <limits>
 
 #include "base/file_path.h"
 #include "base/file_util.h"
@@ skipping 29 matching lines @@
   return cur + size <= end && std::equal(tag, tag + size - 1, cur);
 }
 
 }  // namespace
 
 // static
 bool BlacklistIO::ReadText(Blacklist* blacklist,
                            const FilePath& path,
                            std::string* error_string) {
   DCHECK(blacklist);
+  DCHECK(error_string);
 
   // Memory map for efficient parsing. If the file cannot fit in available
   // memory it would be the least of our worries. Typical blacklist files
   // are less than 200K.
   file_util::MemoryMappedFile input;
   if (!input.Initialize(path) || !input.data()) {
     *error_string = "File I/O error. Check path and permissions.";
     return false;
   }
 
@@ skipping 207 matching lines @@
        i != entries.end(); ++i) {
     if (!output.StoreEntry((*i)->pattern_,
                            (*i)->attributes_,
                            (*i)->types_,
                            index[(*i)->provider_])) {
       return false;
     }
   }
   return true;
 }