Add multiple selection support to chooser on desktops

chrome/browser/chooser_controller/chooser_controller.cc

 // Copyright 2016 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 "chrome/browser/chooser_controller/chooser_controller.h"
 
 #include "base/logging.h"
 #include "base/strings/utf_string_conversions.h"
 #include "components/url_formatter/elide_url.h"
 #include "content/public/browser/render_frame_host.h"
@@ skipping 38 matching lines @@
   return l10n_util::GetStringFUTF16(
       title_string_id_origin_,
       url_formatter::FormatOriginForSecurityDisplay(
           origin, url_formatter::SchemeDisplay::OMIT_CRYPTOGRAPHIC));
 }
 
 bool ChooserController::ShouldShowIconBeforeText() const {
   return false;
 }
 
+bool ChooserController::AllowMultipleSelection() const {
+  return false;
+}
+
 int ChooserController::GetSignalStrengthLevel(size_t index) const {
   return -1;
 }
 
 bool ChooserController::IsConnected(size_t index) const {
   return false;
 }
 
 bool ChooserController::IsPaired(size_t index) const {
   return false;
 }
 
 void ChooserController::OpenAdapterOffHelpUrl() const {
   NOTREACHED();
 }