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

base/threading/thread.h

Index: base/threading/thread.h
===================================================================
--- base/threading/thread.h	(revision 138018)
+++ base/threading/thread.h	(working copy)
@@ -131,8 +131,7 @@
   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
@@ -164,6 +163,9 @@
   // |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_;