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

ui/gfx/screen_mac.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 "ui/gfx/screen.h"
 
 #import <ApplicationServices/ApplicationServices.h>
 #import <Cocoa/Cocoa.h>
 
 #include <map>
 
 #include "base/logging.h"
 #include "base/mac/sdk_forward_declarations.h"
 #include "base/timer/timer.h"
 #include "ui/gfx/display.h"
 #include "ui/gfx/display_change_notifier.h"
 
 namespace {
 
 // The delay to handle the display configuration changes.
 // See comments in ScreenMac::HandleDisplayReconfiguration.
 const int64 kConfigureDelayMs = 500;
 
 gfx::Rect ConvertCoordinateSystem(NSRect ns_rect) {
   // Primary monitor is defined as the monitor with the menubar,
   // which is always at index 0.
-  NSScreen* primary_screen = [[NSScreen screens] objectAtIndex:0];
+  NSScreen* primary_screen = [[NSScreen screens] firstObject];
   float primary_screen_height = [primary_screen frame].size.height;
   gfx::Rect rect(NSRectToCGRect(ns_rect));
   rect.set_y(primary_screen_height - rect.y() - rect.height());
   return rect;
 }
 
 NSScreen* GetMatchingScreen(const gfx::Rect& match_rect) {
   // Default to the monitor with the current keyboard focus, in case
   // |match_rect| is not on any screen at all.
   NSScreen* max_screen = [NSScreen mainScreen];
@@ skipping 13 matching lines @@
 }
 
 gfx::Display GetDisplayForScreen(NSScreen* screen) {
   NSRect frame = [screen frame];
 
   CGDirectDisplayID display_id = [[[screen deviceDescription]
     objectForKey:@"NSScreenNumber"] unsignedIntValue];
 
   gfx::Display display(display_id, gfx::Rect(NSRectToCGRect(frame)));
   NSRect visible_frame = [screen visibleFrame];
-  NSScreen* primary = [[NSScreen screens] objectAtIndex:0];
+  NSScreen* primary = [[NSScreen screens] firstObject];
 
   // Convert work area's coordinate systems.
   if ([screen isEqual:primary]) {
     gfx::Rect work_area = gfx::Rect(NSRectToCGRect(visible_frame));
     work_area.set_y(frame.size.height - visible_frame.origin.y -
                     visible_frame.size.height);
     display.set_work_area(work_area);
   } else {
     display.set_bounds(ConvertCoordinateSystem(frame));
     display.set_work_area(ConvertCoordinateSystem(visible_frame));
@@ skipping 24 matching lines @@
   }
 
   ~ScreenMac() override {
     CGDisplayRemoveReconfigurationCallback(
         ScreenMac::DisplayReconfigurationCallBack, this);
   }
 
   gfx::Point GetCursorScreenPoint() override {
     NSPoint mouseLocation  = [NSEvent mouseLocation];
     // Flip coordinates to gfx (0,0 in top-left corner) using primary screen.
-    NSScreen* screen = [[NSScreen screens] objectAtIndex:0];
+    NSScreen* screen = [[NSScreen screens] firstObject];
     mouseLocation.y = NSMaxY([screen frame]) - mouseLocation.y;
     return gfx::Point(mouseLocation.x, mouseLocation.y);
   }
 
   gfx::NativeWindow GetWindowUnderCursor() override {
     NOTIMPLEMENTED();
     return gfx::NativeWindow();
   }
 
   gfx::NativeWindow GetWindowAtScreenPoint(const gfx::Point& point) override {
@@ skipping 37 matching lines @@
   // Returns the display that most closely intersects the provided bounds.
   gfx::Display GetDisplayMatching(const gfx::Rect& match_rect) const override {
     NSScreen* match_screen = GetMatchingScreen(match_rect);
     return GetDisplayForScreen(match_screen);
   }
 
   // Returns the primary display.
   gfx::Display GetPrimaryDisplay() const override {
     // Primary display is defined as the display with the menubar,
     // which is always at index 0.
-    NSScreen* primary = [[NSScreen screens] objectAtIndex:0];
+    NSScreen* primary = [[NSScreen screens] firstObject];
     gfx::Display display = GetDisplayForScreen(primary);
     return display;
   }
 
   void AddObserver(gfx::DisplayObserver* observer) override {
     change_notifier_.AddObserver(observer);
   }
 
   void RemoveObserver(gfx::DisplayObserver* observer) override {
     change_notifier_.RemoveObserver(observer);
@@ skipping 98 matching lines @@
 
 namespace gfx {
 
 #if !defined(USE_AURA)
 Screen* CreateNativeScreen() {
   return new ScreenMac;
 }
 #endif
 
 }