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

chrome/browser/ui/cocoa/browser_window_cocoa.mm

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/ui/cocoa/browser_window_cocoa.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/logging.h"
 #import "base/mac/sdk_forward_declarations.h"
@@ skipping 192 matching lines @@
 }
 
 void BrowserWindowCocoa::SetBounds(const gfx::Rect& bounds) {
   gfx::Rect real_bounds = [controller_ enforceMinWindowSize:bounds];
 
   ExitFullscreen();
   NSRect cocoa_bounds = NSMakeRect(real_bounds.x(), 0,
                                    real_bounds.width(),
                                    real_bounds.height());
   // Flip coordinates based on the primary screen.
-  NSScreen* screen = [[NSScreen screens] objectAtIndex:0];
+  NSScreen* screen = [[NSScreen screens] firstObject];
   cocoa_bounds.origin.y =
       NSHeight([screen frame]) - real_bounds.height() - real_bounds.y();
 
   [window() setFrame:cocoa_bounds display:YES];
 }
 
 // Callers assume that this doesn't immediately delete the Browser object.
 // The controller implementing the window delegate methods called from
 // |-performClose:| must take precautions to ensure that.
 void BrowserWindowCocoa::Close() {
@@ skipping 117 matching lines @@
   // way views and GTK do.
   // See http://crbug.com/340720 for discussion.
 }
 
 void BrowserWindowCocoa::ZoomChangedForActiveTab(bool can_show_bubble) {
   [controller_ zoomChangedForActiveTab:can_show_bubble ? YES : NO];
 }
 
 gfx::Rect BrowserWindowCocoa::GetRestoredBounds() const {
   // Flip coordinates based on the primary screen.
-  NSScreen* screen = [[NSScreen screens] objectAtIndex:0];
+  NSScreen* screen = [[NSScreen screens] firstObject];
   NSRect frame = [controller_ regularWindowFrame];
   gfx::Rect bounds(frame.origin.x, 0, NSWidth(frame), NSHeight(frame));
   bounds.set_y(NSHeight([screen frame]) - NSMaxY(frame));
   return bounds;
 }
 
 ui::WindowShowState BrowserWindowCocoa::GetRestoredState() const {
   if (IsMaximized())
     return ui::SHOW_STATE_MAXIMIZED;
   if (IsMinimized())
@@ skipping 492 matching lines @@
 void BrowserWindowCocoa::UnhideDownloadShelf() {
   GetDownloadShelf()->Unhide();
 }
 
 void BrowserWindowCocoa::HideDownloadShelf() {
   GetDownloadShelf()->Hide();
   StatusBubble* statusBubble = GetStatusBubble();
   if (statusBubble)
     statusBubble->Hide();
 }