Base: Don't overwrite the thread id when ThreadMain exits. There's

base/threading/thread.h

 // Copyright (c) 2012 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 BASE_THREAD_H_
 #define BASE_THREAD_H_
 #pragma once
 
 #include <string>
 
@@ skipping 113 matching lines @@
   // Returns the name of this thread (for display in debugger too).
   const std::string &thread_name() { return name_; }
 
   // The native thread handle.
   PlatformThreadHandle thread_handle() { return thread_; }
 
   // The thread ID.
   PlatformThreadId thread_id() const { return thread_id_; }
 
   // Returns true if the thread has been started, and not yet stopped.
-  // When a thread is running, |thread_id_| is a valid id.
-  bool IsRunning() const { return thread_id_ != kInvalidThreadId; }
+  bool IsRunning() const;
 
  protected:
   // Called just prior to starting the message loop
   virtual void Init() {}
 
   // Called to start the message loop
   virtual void Run(MessageLoop* message_loop);
 
   // Called just after the message loop ends
   virtual void CleanUp() {}
@@ skipping 11 matching lines @@
   // PlatformThread::Delegate methods:
   virtual void ThreadMain() OVERRIDE;
 
   // Whether we successfully started the thread.
   bool started_;
 
   // If true, we're in the middle of stopping, and shouldn't access
   // |message_loop_|. It may non-NULL and invalid.
   bool stopping_;
 
+  // True while inside of Run().
+  bool running_;
+
   // Used to pass data to ThreadMain.
   struct StartupData;
   StartupData* startup_data_;
 
   // The thread's handle.
   PlatformThreadHandle thread_;
 
   // The thread's message loop.  Valid only while the thread is alive.  Set
   // by the created thread.
   MessageLoop* message_loop_;
 
   // Our thread's ID.
   PlatformThreadId thread_id_;
 
   // The name of the thread.  Used for debugging purposes.
   std::string name_;
 
   friend void ThreadQuitHelper();
 
   DISALLOW_COPY_AND_ASSIGN(Thread);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREAD_H_