Stop base::OpenFile from leaking fds/handles into child procs.

base/files/file_util_win.cc

Index: base/files/file_util_win.cc
diff --git a/base/files/file_util_win.cc b/base/files/file_util_win.cc
index 4e67b5a348653f3af41d897f845ce4e0df4f2571..87c0e8e7af16121457452ff78d362d9e4cad6c02 100644
--- a/base/files/file_util_win.cc
+++ b/base/files/file_util_win.cc
@@ -70,6 +70,14 @@ bool DeleteFileRecursive(const FilePath& path,
   return true;
 }
 
+// Appends |mode_char| to |mode| before the optional character set encoding; see
+// https://msdn.microsoft.com/library/yeby3zcb.aspx for details.
+void AppendModeCharacter(base::char16 mode_char, base::string16* mode) {
+  size_t comma_pos = mode->find(L',');
+  mode->insert(comma_pos == base::string16::npos ? mode->length() : comma_pos,
+               1, mode_char);
+}
+
 }  // namespace
 
 FilePath MakeAbsoluteFilePath(const FilePath& input) {
@@ -586,8 +594,14 @@ bool GetFileInfo(const FilePath& file_path, File::Info* results) {
 }
 
 FILE* OpenFile(const FilePath& filename, const char* mode) {
+  // 'N' is unconditionally added below, so be sure there is not one already
+  // present before a comma in |mode|.
+  DCHECK(
+      strchr(mode, 'N') == nullptr ||
+      (strchr(mode, ',') != nullptr && strchr(mode, 'N') > strchr(mode, ',')));
   ThreadRestrictions::AssertIOAllowed();
   string16 w_mode = ASCIIToUTF16(mode);
+  AppendModeCharacter(L'N', &w_mode);
   return _wfsopen(filename.value().c_str(), w_mode.c_str(), _SH_DENYNO);
 }