[Mac] Fix a potential crash in the permission bubble controller

chrome/browser/ui/cocoa/permission_bubble/permission_bubble_controller.mm

 // Copyright 2014 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/permission_bubble/permission_bubble_controller.h"
 
 #include <algorithm>
 
 #include "base/mac/bind_objc_block.h"
 #include "base/macros.h"
@@ skipping 264 matching lines @@
 - (void)windowWillClose:(NSNotification*)notification {
   [[NSNotificationCenter defaultCenter]
       removeObserver:self
                 name:NSWindowDidMoveNotification
               object:nil];
   bridge_->OnBubbleClosing();
   [super windowWillClose:notification];
 }
 
 - (void)showWindow:(id)sender {
-  if ([self hasVisibleLocationBar]) {
-    decoration_ = [[self.parentWindow windowController] locationBarBridge]
-                      ->GetPageInfoDecoration();
+  LocationBarViewMac* bridge =
+      [[self.parentWindow windowController] locationBarBridge];
+  if ([self hasVisibleLocationBar] && bridge) {
+    decoration_ = bridge->GetPageInfoDecoration();
     decoration_->SetActive(true);
   }
 
   [super showWindow:sender];
 }
 
 - (void)close {
   if (decoration_) {
     decoration_->SetActive(false);
     decoration_ = nullptr;
@@ skipping 359 matching lines @@
 }
 
 - (IBAction)cancel:(id)sender {
   // This is triggered by ESC when the bubble has focus.
   if (delegate_)
     delegate_->Closing();
   [super cancel:sender];
 }
 
 @end  // implementation PermissionBubbleController