Enable "Hide Extension" option when "Save Link As" on the Mac

ui/shell_dialogs/select_file_dialog_mac.mm

 // 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 "ui/shell_dialogs/select_file_dialog.h"
 
 #import <Cocoa/Cocoa.h>
 #include <CoreServices/CoreServices.h>
 
 #include <map>
 #include <set>
 #include <vector>
 
 #include "base/files/file_util.h"
 #include "base/logging.h"
 #include "base/mac/bundle_locations.h"
 #include "base/mac/foundation_util.h"
 #include "base/mac/scoped_cftyperef.h"
 #import "base/mac/scoped_nsobject.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/threading/thread_restrictions.h"
 #import "ui/base/cocoa/nib_loading.h"
 #include "ui/base/l10n/l10n_util_mac.h"
+#include "ui/shell_dialogs/selected_file_info.h"
 #include "ui/strings/grit/ui_strings.h"
 
 namespace {
 
 const int kFileTypePopupTag = 1234;
 
 CFStringRef CreateUTIFromExtension(const base::FilePath::StringType& ext) {
   base::ScopedCFTypeRef<CFStringRef> ext_cf(base::SysUTF8ToCFStringRef(ext));
   return UTTypeCreatePreferredIdentifierForTag(
       kUTTagClassFilenameExtension, ext_cf.get(), NULL);
@@ skipping 109 matching lines @@
 
   if (!listener_)
     return;
 
   if (was_cancelled || files.empty()) {
     listener_->FileSelectionCanceled(params);
   } else {
     if (is_multi) {
       listener_->MultiFilesSelected(files, params);
     } else {
-      listener_->FileSelected(files[0], index, params);
+      ui::SelectedFileInfo file(files[0], base::FilePath());
+      if ([dialog isExtensionHidden]) {

[asanka, 2015/12/16 02:54:26]

Doesn't this mean that the user has chosen to expose or hide extensions in the
NSSavePanel (i.e. a setting that's ephemeral and only applying to save dialogs
for Chrome/Chromium)? Why do we need to use it to set the NSFileExtensionHidden
attribute on the file on disk?

[shrike, 2015/12/16 19:04:12]

The "Hide Extension" checkbox does not hide extensions in the NSSavePanel
(notice that toggling it does not hide the file extensions of files listed in
the file browser). Rather, it is an option that allows the user to say whether
or not they want the file extension visible for the file they are about to
create. It is then up to the application to hide the extension once the file has
been created.

+        file.SetHideFileExtension(true);
+      }
+      listener_->FileSelectedWithExtraInfo(file, index, params);
     }
   }
 }
 
 void SelectFileDialogImpl::SelectFileImpl(
     Type type,
     const base::string16& title,
     const base::FilePath& default_path,
     const FileTypeInfo* file_types,
     int file_type_index,
@@ skipping 256 matching lines @@
 
 namespace ui {
 
 SelectFileDialog* CreateMacSelectFileDialog(
     SelectFileDialog::Listener* listener,
     SelectFilePolicy* policy) {
   return new SelectFileDialogImpl(listener, policy);
 }
 
 }  // namespace ui