Check if BubbleReference weak pointer is valid before using it in the chooser

chrome/browser/ui/cocoa/website_settings/chooser_bubble_ui_cocoa.mm

 // 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.
 
 #import "chrome/browser/ui/cocoa/website_settings/chooser_bubble_ui_cocoa.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <cmath>
@@ skipping 248 matching lines @@
   NSRect frameA = [viewA frame];
   NSRect frameB = [viewB frame];
   frameA.origin.y =
       NSMinY(frameB) + std::floor((NSHeight(frameB) - NSHeight(frameA)) / 2);
   [viewA setFrameOrigin:frameA.origin];
 }
 
 - (void)onConnect:(id)sender {
   buttonPressed_ = true;
   [chooserContentView_ accept];
-  self.bubbleReference->CloseBubble(BUBBLE_CLOSE_ACCEPTED);
+  if (self.bubbleReference)
+    self.bubbleReference->CloseBubble(BUBBLE_CLOSE_ACCEPTED);
   [self close];
 }
 
 - (void)onCancel:(id)sender {
   buttonPressed_ = true;
   [chooserContentView_ cancel];
-  self.bubbleReference->CloseBubble(BUBBLE_CLOSE_CANCELED);
+  if (self.bubbleReference)
+    self.bubbleReference->CloseBubble(BUBBLE_CLOSE_CANCELED);
   [self close];
 }
 
 @end
 
 ChooserBubbleUiCocoa::ChooserBubbleUiCocoa(
     Browser* browser,
     std::unique_ptr<ChooserController> chooser_controller)
     : browser_(browser),
       chooser_bubble_ui_controller_(nil) {
@@ skipping 26 matching lines @@
 }
 
 void ChooserBubbleUiCocoa::UpdateAnchorPosition() {
   if (chooser_bubble_ui_controller_)
     [chooser_bubble_ui_controller_ updateAnchorPosition];
 }
 
 void ChooserBubbleUiCocoa::OnBubbleClosing() {
   chooser_bubble_ui_controller_ = nil;
 }