Pass a BubbleReference to BubbleUI::Show.

components/bubble.gypi

 # Copyright 2015 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.
 
 {
   'targets': [
     {
       # GN version: //components/bubble
       'target_name': 'bubble',
       'type': 'static_library',
       'include_dirs': [
         '..',
       ],
       'sources': [
         # Note: sources list duplicated in GN build.
         'bubble/bubble_close_reason.h',
         'bubble/bubble_controller.cc',
         'bubble/bubble_controller.h',
         'bubble/bubble_delegate.cc',
         'bubble/bubble_delegate.h',
         'bubble/bubble_manager.cc',
         'bubble/bubble_manager.h',
+        'bubble/bubble_reference.h',
         'bubble/bubble_ui.h',
       ],
     },
   ],
 }