(not for review): PlatformThreadHandle: remove public id() interface

base/threading/thread.h

Index: base/threading/thread.h
diff --git a/base/threading/thread.h b/base/threading/thread.h
index 5126491b3861cdb60f23eec1b40b11466d27a33a..afefe5c5f7628d7fe2ed6567cd3aec66e77cf01b 100644
--- a/base/threading/thread.h
+++ b/base/threading/thread.h
@@ -14,12 +14,12 @@
 #include "base/message_loop/timer_slack.h"
 #include "base/single_thread_task_runner.h"
 #include "base/synchronization/lock.h"
+#include "base/synchronization/waitable_event.h"
 #include "base/threading/platform_thread.h"
 
 namespace base {
 
 class MessagePump;
-class WaitableEvent;
 
 // A simple thread abstraction that establishes a MessageLoop on a new thread.
 // The consumer uses the MessageLoop of the thread to cause code to execute on
@@ -170,7 +170,7 @@ class BASE_EXPORT Thread : PlatformThread::Delegate {
   // The native thread handle.
   PlatformThreadHandle thread_handle() { return thread_; }
 
-  // The thread ID.
+  // The thread ID. Should not be called before Start*().
   PlatformThreadId thread_id() const;
 
   // Returns true if the thread has been started, and not yet stopped.
@@ -222,6 +222,11 @@ class BASE_EXPORT Thread : PlatformThread::Delegate {
   PlatformThreadHandle thread_;
   mutable base::Lock thread_lock_;  // Protects thread_.
 
+  // The thread's id once it was started.
+  PlatformThreadId id_;
+
+  mutable WaitableEvent id_event_;  // Protects id_.
+
   // The thread's message loop.  Valid only while the thread is alive.  Set
   // by the created thread.
   MessageLoop* message_loop_;