Add multiple selection support to chooser on desktops

chrome/browser/chooser_controller/chooser_controller.h

 // 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.
 
 #ifndef CHROME_BROWSER_CHOOSER_CONTROLLER_CHOOSER_CONTROLLER_H_
 #define CHROME_BROWSER_CHOOSER_CONTROLLER_CHOOSER_CONTROLLER_H_
 
 #include "base/macros.h"
 #include "base/strings/string16.h"
 
@@ skipping 48 matching lines @@
     virtual ~View() {}
   };
 
   // Returns the text to be displayed in the chooser title.
   base::string16 GetTitle() const;
 
   // Returns if the chooser needs to show an icon before the text.
   // For WebBluetooth, it is a signal strength icon.
   virtual bool ShouldShowIconBeforeText() const;
 
+  // Returns if the chooser allows multiple items to be selected.
+  virtual bool AllowMultipleSelection() const;
+
   // Returns the text to be displayed in the chooser when there are no options.
   virtual base::string16 GetNoOptionsText() const = 0;
 
   // Returns the label for OK button.
   virtual base::string16 GetOkButtonLabel() const = 0;
 
   // The number of options users can pick from. For example, it can be
   // the number of USB/Bluetooth device names which are listed in the
   // chooser so that users can grant permission.
   virtual size_t NumOptions() const = 0;
@@ skipping 45 matching lines @@
  private:
   content::RenderFrameHost* const owning_frame_;
   const int title_string_id_origin_;
   const int title_string_id_extension_;
   View* view_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(ChooserController);
 };
 
 #endif  // CHROME_BROWSER_CHOOSER_CONTROLLER_CHOOSER_CONTROLLER_H_