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

chrome/browser/ui/cocoa/autofill/autofill_popup_base_view_cocoa.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/autofill/autofill_popup_base_view_cocoa.h"
 
 #include "chrome/browser/ui/autofill/autofill_popup_view_delegate.h"
 #include "chrome/browser/ui/autofill/popup_constants.h"
 #include "ui/base/cocoa/window_size_constants.h"
 
@@ skipping 121 matching lines @@
 #pragma mark -
 #pragma mark Messages from AutofillPopupViewBridge:
 
 - (void)updateBoundsAndRedrawPopup {
   NSRect frame = NSRectFromCGRect(delegate_->popup_bounds().ToCGRect());
 
   // Flip coordinates back into Cocoa-land.  The controller's platform-neutral
   // coordinate space places the origin at the top-left of the first screen,
   // whereas Cocoa's coordinate space expects the origin to be at the
   // bottom-left of this same screen.
-  NSScreen* screen = [[NSScreen screens] objectAtIndex:0];
+  NSScreen* screen = [[NSScreen screens] firstObject];
   frame.origin.y = NSMaxY([screen frame]) - NSMaxY(frame);
 
   // TODO(isherman): The view should support scrolling if the popup gets too
   // big to fit on the screen.
   [[self window] setFrame:frame display:YES];
   [self setNeedsDisplay:YES];
 }
 
 - (void)showPopup {
   NSWindow* window =
@@ skipping 13 matching lines @@
 
 - (void)hidePopup {
   // Remove the child window before closing, otherwise it can mess up
   // display ordering.
   NSWindow* window = [self window];
   [[window parentWindow] removeChildWindow:window];
   [window close];
 }
 
 @end