Mac: Use [NSArray firstObject] for [NSScreen screens]

chrome/browser/ui/cocoa/autofill/autofill_section_container.mm

 // Copyright (c) 2013 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/autofill/autofill_section_container.h"
 
 #include <algorithm>
 
 #include "base/mac/foundation_util.h"
 #include "base/strings/sys_string_conversions.h"
@@ skipping 388 matching lines @@
                         edited:(BOOL)edited {
   autofill::ServerFieldType type = [self fieldTypeForControl:field];
   base::string16 fieldValue = base::SysNSStringToUTF16([field fieldValue]);
 
   // Get the frame rectangle for the designated field, in screen coordinates.
   NSRect textFrameInScreen = [field convertRect:[field bounds] toView:nil];
   textFrameInScreen.origin =
       [[field window] convertBaseToScreen:textFrameInScreen.origin];
 
   // And adjust for gfx::Rect being flipped compared to OSX coordinates.
-  NSScreen* screen = [[NSScreen screens] objectAtIndex:0];
+  NSScreen* screen = [[NSScreen screens] firstObject];
   textFrameInScreen.origin.y =
       NSMaxY([screen frame]) - NSMaxY(textFrameInScreen);
   gfx::Rect textFrameRect(NSRectToCGRect(textFrameInScreen));
 
   delegate_->UserEditedOrActivatedInput(section_,
                                         type,
                                         [self view],
                                         textFrameRect,
                                         fieldValue,
                                         edited);
@@ skipping 327 matching lines @@
 
 - (void)activateFieldForType:(autofill::ServerFieldType)type {
   NSControl<AutofillInputField>* field = [inputs_ viewWithTag:type];
   if (field) {
     [[field window] makeFirstResponder:field];
     [self fieldEditedOrActivated:field edited:NO];
   }
 }
 
 @end