GN: Enable ARC for Mac and iOS in rtc_* templates

webrtc/modules/desktop_capture/mouse_cursor_monitor_mac.mm

 /*
  *  Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 19 matching lines @@
 
 namespace webrtc {
 
 namespace {
 // Paint the image, so that we can get a bitmap representation compatible with
 // current context. For example, in the retina display, we are going to get an
 // image with same visual size but underlying pixel size conforms to the retina
 // setting.
 NSImage* PaintInCurrentContext(NSImage* source) {
   NSSize size = [source size];
-  NSImage* new_image = [[[NSImage alloc] initWithSize:size] autorelease];
+  NSImage* new_image = [[NSImage alloc] initWithSize:size];
   [new_image lockFocus];
   NSRect frame = NSMakeRect(0, 0, size.width, size.height);
   [source drawInRect:frame
             fromRect:frame
            operation:NSCompositeCopy
             fraction:1.0];
   [new_image unlockFocus];
   return new_image;
 }
 }  // namespace
@@ skipping 267 matching lines @@
   return new MouseCursorMonitorMac(options, window, kInvalidScreenId);
 }
 
 MouseCursorMonitor* MouseCursorMonitor::CreateForScreen(
     const DesktopCaptureOptions& options,
     ScreenId screen) {
   return new MouseCursorMonitorMac(options, kCGNullWindowID, screen);
 }
 
 }  // namespace webrtc