Pass a BubbleReference to BubbleUI::Show.

components/bubble/BUILD.gn

 # 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.
 
 source_set("bubble") {
   sources = [
     "bubble_close_reason.h",
     "bubble_controller.cc",
     "bubble_controller.h",
     "bubble_delegate.cc",
     "bubble_delegate.h",
     "bubble_manager.cc",
     "bubble_manager.h",
+    "bubble_reference.h",
     "bubble_ui.h",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
 
   sources = [
     "bubble_manager_unittest.cc",
   ]
 
   deps = [
     ":bubble",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }