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

ui/shell_dialogs/select_file_dialog_mac.mm

Index: ui/shell_dialogs/select_file_dialog_mac.mm
diff --git a/ui/shell_dialogs/select_file_dialog_mac.mm b/ui/shell_dialogs/select_file_dialog_mac.mm
index 9a4a5fd386792122f0c7d6a3ad1832d97f5f26a9..6ba1f0d1ce74045cdb9b7275c553e1961d57293e 100644
--- a/ui/shell_dialogs/select_file_dialog_mac.mm
+++ b/ui/shell_dialogs/select_file_dialog_mac.mm
@@ -21,6 +21,7 @@
 #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 {
@@ -150,7 +151,11 @@ void SelectFileDialogImpl::FileWasSelected(
     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);
     }
   }
 }