Move platform_thread to base/threading and put in the base namespace. I left ...

base/threading/platform_thread_mac.mm

-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2010 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 "base/platform_thread.h"
+#include "base/threading/platform_thread.h"
 
 #import <Foundation/Foundation.h>
 #include <dlfcn.h>
 
 #include "base/logging.h"
 
 namespace base {
 
 // If Cocoa is to be used on more than one thread, it must know that the
 // application is multithreaded.  Since it's possible to enter Cocoa code
 // from threads created by pthread_thread_create, Cocoa won't necessarily
 // be aware that the application is multithreaded.  Spawning an NSThread is
 // enough to get Cocoa to set up for multithreaded operation, so this is done
 // if necessary before pthread_thread_create spawns any threads.
 //
 // http://developer.apple.com/documentation/Cocoa/Conceptual/Multithreading/CreatingThreads/chapter_4_section_4.html
 void InitThreading() {
   static BOOL multithreaded = [NSThread isMultiThreaded];
   if (!multithreaded) {
     // +[NSObject class] is idempotent.
     [NSThread detachNewThreadSelector:@selector(class)
                              toTarget:[NSObject class]
                            withObject:nil];
     multithreaded = YES;
 
     DCHECK([NSThread isMultiThreaded]);
   }
 }
 
-}  // namespace base
-
 // static
 void PlatformThread::SetName(const char* name) {
   // pthread_setname_np is only available in 10.6 or later, so test
   // for it at runtime.
   int (*dynamic_pthread_setname_np)(const char*);
   *reinterpret_cast<void**>(&dynamic_pthread_setname_np) =
       dlsym(RTLD_DEFAULT, "pthread_setname_np");
   if (!dynamic_pthread_setname_np)
     return;
 
   // Mac OS X does not expose the length limit of the name, so
   // hardcode it.
   const int kMaxNameLength = 63;
   std::string shortened_name = std::string(name).substr(0, kMaxNameLength);
   // pthread_setname() fails (harmlessly) in the sandbox, ignore when it does.
   // See http://crbug.com/47058
   dynamic_pthread_setname_np(shortened_name.c_str());
 }
+
+}  // namespace base