Avoid using WTF threading code in cc

cc/CCThread.h

 // Copyright 2011 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.
 
 #ifndef CCThread_h
 #define CCThread_h
 
+#include "base/threading/platform_thread.h"
 #include <wtf/PassOwnPtr.h>
-#include <wtf/Threading.h>
+#include <wtf/Noncopyable.h>
 
 namespace WebCore {
 
 // CCThread provides basic infrastructure for messaging with the compositor in a
 // platform-neutral way.
 class CCThread {
 public:
     virtual ~CCThread() { }
 
     class Task {
         WTF_MAKE_NONCOPYABLE(Task);
     public:
         virtual ~Task() { }
         virtual void performTask() = 0;
         void* instance() const { return m_instance; }
     protected:
         Task(void* instance) : m_instance(instance) { }
         void* m_instance;
     };
 
     // Executes the task on context's thread asynchronously.
     virtual void postTask(PassOwnPtr<Task>) = 0;
 
     // Executes the task after the specified delay.
     virtual void postDelayedTask(PassOwnPtr<Task>, long long delayMs) = 0;
 
-    virtual WTF::ThreadIdentifier threadID() const = 0;
+    virtual base::PlatformThreadId threadID() const = 0;
 };
 
 }
 
 #endif