Add WIN_ prefix to Windows-specific base::File flags.

This brings documentation about the flaghs being Windows-only to
the callsites, making the behavior clearer to the calling code.

This is the initial CL that only adds aliases for these flags and
updates references from base/files. The plan is to then send
individual CLs (via git cl split) to migrate call sites, so that
callers have a chance to review their usage for correctness.

Bug: 1244149
Change-Id: I61f63ad5c0a5fff989f3cdc73f67c0f942134c5a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3227343
Reviewed-by: Gabriel Charette <gab@chromium.org>
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/main@{#933879}

diff --git a/base/files/file_util.cc b/base/files/file_util.cc
index 7ce17b00..7058010 100644
--- a/base/files/file_util.cc
+++ b/base/files/file_util.cc

@@ -321,12 +321,12 @@
 bool TouchFile(const FilePath& path,
                const Time& last_accessed,
                const Time& last_modified) {
-  int flags = File::FLAG_OPEN | File::FLAG_WRITE_ATTRIBUTES;
+  int flags = File::FLAG_OPEN | File::FLAG_WIN_WRITE_ATTRIBUTES;
 
 #if defined(OS_WIN)
   // On Windows, FILE_FLAG_BACKUP_SEMANTICS is needed to open a directory.
   if (DirectoryExists(path))
-    flags |= File::FLAG_BACKUP_SEMANTICS;
+    flags |= File::FLAG_WIN_BACKUP_SEMANTICS;
 #elif defined(OS_FUCHSIA)
   // On Fuchsia, we need O_RDONLY for directories, or O_WRONLY for files.
   // TODO(https://crbug.com/947802): Find a cleaner workaround for this.
@@ -407,8 +407,8 @@
   DCHECK_GE(max_bytes, 0);
 
   File file(file_path, File::FLAG_OPEN | File::FLAG_READ |
-                           File::FLAG_SEQUENTIAL_SCAN |
-                           File::FLAG_SHARE_DELETE);
+                           File::FLAG_WIN_SEQUENTIAL_SCAN |
+                           File::FLAG_WIN_SHARE_DELETE);
   if (!file.IsValid())
     return false;