Firefox overlay is seen opened even if Import Overlay is Cancelled.

chrome/browser/ui/cocoa/importer/import_lock_dialog_cocoa.mm

Index: chrome/browser/ui/cocoa/importer/import_lock_dialog_cocoa.mm
diff --git a/chrome/browser/ui/cocoa/importer/import_lock_dialog_cocoa.mm b/chrome/browser/ui/cocoa/importer/import_lock_dialog_cocoa.mm
index 45b25e91b480f787e2a2314f291a6f80d67773d2..1c594e9d41b8d533372b4687b6f6e186d44b3e60 100644
--- a/chrome/browser/ui/cocoa/importer/import_lock_dialog_cocoa.mm
+++ b/chrome/browser/ui/cocoa/importer/import_lock_dialog_cocoa.mm
@@ -18,9 +18,11 @@ using base::UserMetricsAction;
 
 namespace importer {
 
+base::scoped_nsobject<NSAlert> lock_alert;
+
 void ShowImportLockDialog(gfx::NativeWindow parent,
                           const base::Callback<void(bool)>& callback) {
-  base::scoped_nsobject<NSAlert> lock_alert([[NSAlert alloc] init]);
+  lock_alert.reset([[NSAlert alloc] init]);
   [lock_alert addButtonWithTitle:l10n_util::GetNSStringWithFixup(
       IDS_IMPORTER_LOCK_OK)];
   [lock_alert addButtonWithTitle:l10n_util::GetNSStringWithFixup(
@@ -36,4 +38,9 @@ void ShowImportLockDialog(gfx::NativeWindow parent,
   content::RecordAction(UserMetricsAction("ImportLockDialogCocoa_Shown"));
 }
 
+void HideImportLockDialog() {
+  [NSApp endSheet:[lock_alert window]];
+  lock_alert.reset();

[Ilya Sherman, 2017/03/29 06:29:02]

I just tested this on my Mac, and I couldn't actually reproduce the original
bug.  AFAICT, while the sheet is showing, there is no way to close the parent
dialog.  So, you could probably actually leave this method body empty, with a
comment explaining that there is no need for this code path on Mac.

[nikhil.sahni, 2017/03/30 12:13:35]

Done.

+}
+
 }  // namespace importer