[Mac] Fix accessibility crash because I am terrible with dynamic types.

chrome/browser/ui/cocoa/profiles/profile_chooser_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 <Cocoa/Cocoa.h>
 
 #import "chrome/browser/ui/cocoa/profiles/profile_chooser_controller.h"
 
 #include "base/mac/bundle_locations.h"
 #include "base/prefs/pref_service.h"
@@ skipping 755 matching lines @@
 @interface DummyWindowFocusButton : NSButton
 @end
 
 @implementation DummyWindowFocusButton
 // Ignore accessibility, as this is a placeholder button.
 - (BOOL)accessibilityIsIgnored {
   return YES;
 }
 
 - (id)accessibilityAttributeValue:(NSString*)attribute {
-  return @[];
+  return nil;
 }
 
 - (BOOL)canBecomeKeyView {
   return false;
 }
 
 @end
 
 @interface ProfileChooserController ()
 // Builds the profile chooser view.
@@ skipping 358 matching lines @@
       break;
   }
 
   // Clears tutorial mode for all non-profile-chooser views.
   if (viewMode_ != profiles::BUBBLE_VIEW_MODE_PROFILE_CHOOSER)
     tutorialMode_ = profiles::TUTORIAL_MODE_NONE;
 
   // Add a dummy, empty element so that we don't initially display any
   // focus rings.
   NSButton* dummyFocusButton =
-      [[[DummyWindowFocusButton alloc] initWithFrame:NSZeroRect] autorelease];
+     [[[DummyWindowFocusButton alloc] initWithFrame:NSZeroRect] autorelease];
   [dummyFocusButton setNextKeyView:subView];
   [[self window] makeFirstResponder:dummyFocusButton];
 
   [contentView addSubview:subView];
   [contentView addSubview:dummyFocusButton];
   SetWindowSize([self window],
       NSMakeSize(NSWidth([subView frame]), NSHeight([subView frame])));
 }
 
 - (NSView*)buildProfileChooserView {
@@ skipping 1026 matching lines @@
 }
 
 - (bool)shouldShowGoIncognito {
   bool incognitoAvailable =
       IncognitoModePrefs::GetAvailability(browser_->profile()->GetPrefs()) !=
           IncognitoModePrefs::DISABLED;
   return incognitoAvailable && !browser_->profile()->IsGuestSession();
 }
 
 @end