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

base/cancellation_flag.h

Index: base/cancellation_flag.h
===================================================================
--- base/cancellation_flag.h	(revision 70328)
+++ base/cancellation_flag.h	(working copy)
@@ -1,4 +1,4 @@
-// Copyright (c) 2009 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.
 
@@ -7,7 +7,7 @@
 #pragma once
 
 #include "base/atomicops.h"
-#include "base/platform_thread.h"
+#include "base/threading/platform_thread.h"
 
 namespace base {