Truncate the download file name if it exceeds the filesystem limit.

base/file_util_posix.cc

 // 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.
 
 #include "base/file_util.h"
 
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <fnmatch.h>
@@ skipping 1112 matching lines @@
     }
 
     allowed_group_ids.insert(group_record->gr_gid);
   }
 
   return VerifyPathControlledByUser(
       kFileSystemRoot, path, kRootUid, allowed_group_ids);
 }
 #endif  // defined(OS_MACOSX) && !defined(OS_IOS)
 
+int GetMaximumPathComponentLength(const FilePath& path) {
+  base::ThreadRestrictions::AssertIOAllowed();
+  return pathconf(path.value().c_str(), _PC_NAME_MAX);
+}
+
 }  // namespace file_util