Replace some deprecated usages of readdir_r with readdir

base/files/file_enumerator_posix.cc

Index: base/files/file_enumerator_posix.cc
diff --git a/base/files/file_enumerator_posix.cc b/base/files/file_enumerator_posix.cc
index fb4010aadcad566f304a899344f1cb892b666081..16a04801c3ae450f5ad6c88a02571f12f5cdabde 100644
--- a/base/files/file_enumerator_posix.cc
+++ b/base/files/file_enumerator_posix.cc
@@ -131,9 +131,11 @@ bool FileEnumerator::ReadDirectory(std::vector<FileInfo>* entries,
          additional space for pathname may be needed
 #endif
 
-  struct dirent dent_buf;
-  struct dirent* dent;
-  while (readdir_r(dir, &dent_buf, &dent) == 0 && dent) {
+  // In all implementations of the C library that Chromium can run with,
+  // concurrent calls to readdir that specify different directory streams are
+  // thread-safe. This is the case here, since the directory stream is scoped to
+  // the current function. See https://codereview.chromium.org/2411833004/#msg3
+  for (struct dirent* dent = readdir(dir); dent; dent = readdir(dir)) {
     FileInfo info;
     info.filename_ = FilePath(dent->d_name);