Add Darwin thread.h implementation.

webrtc/base/maccocoathreadhelper.mm

-/*
- *  Copyright 2007 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.
- */
-// Helper function for using Cocoa with Posix threading.
-
-#import <Foundation/Foundation.h>
-
-#import "webrtc/base/maccocoathreadhelper.h"
-
-#include "webrtc/base/checks.h"
-
-namespace rtc {
-
-// Cocoa must be "put into multithreading mode" before Cocoa functionality can
-// be used on POSIX threads. The way to do that is to spawn one thread that may
-// immediately exit.
-void InitCocoaMultiThreading() {
-  if ([NSThread isMultiThreaded] == NO) {
-    // The sole purpose of this autorelease pool is to avoid a console
-    // message on Leopard that tells us we're autoreleasing the thread
-    // with no autorelease pool in place.
-    // Doing NSAutoreleasePool* hack = [[NSAutoreleasePool alloc] init];
-    // causes unused variable error.
-    NSAutoreleasePool* hack;
-    hack = [[NSAutoreleasePool alloc] init];
-    [NSThread detachNewThreadSelector:@selector(class)
-                             toTarget:[NSObject class]
-                           withObject:nil];
-    [hack drain];
-  }
-
-  RTC_DCHECK([NSThread isMultiThreaded]);
-}
-
-}  // namespace rtc