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

base/files/file_util.h

Index: base/files/file_util.h
diff --git a/base/files/file_util.h b/base/files/file_util.h
index 77a87e7dade7df8db204dfd33aaafe7209c8a06b..5ada35f9a447a3b257dd78ef60bc8d514a0f40db 100644
--- a/base/files/file_util.h
+++ b/base/files/file_util.h
@@ -307,7 +307,9 @@ BASE_EXPORT bool TouchFile(const FilePath& path,
                            const Time& last_accessed,
                            const Time& last_modified);
 
-// Wrapper for fopen-like calls. Returns non-NULL FILE* on success.
+// Wrapper for fopen-like calls. Returns non-NULL FILE* on success. The
+// underlying file descriptor (POSIX) or handle (Windows) is unconditionally
+// configured to not be propagated to child processes.
 BASE_EXPORT FILE* OpenFile(const FilePath& filename, const char* mode);
 
 // Closes file opened by OpenFile. Returns true on success.