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..929828bf49872c878eb3fa5716d17daf44132d3a 100644
--- a/base/threading/thread.h
+++ b/base/threading/thread.h
@@ -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. Only valid after this Thread was started.
   PlatformThreadId thread_id() const;
 
   // Returns true if the thread has been started, and not yet stopped.
@@ -216,11 +216,15 @@ class BASE_EXPORT Thread : PlatformThread::Delegate {
 
   // True while inside of Run().
   bool running_;
-  mutable base::Lock running_lock_;  // Protects running_.
+  mutable base::Lock running_lock_;  // Protects |running_|.
 
   // The thread's handle.
   PlatformThreadHandle thread_;
-  mutable base::Lock thread_lock_;  // Protects thread_.
+  mutable base::Lock thread_lock_;  // Protects |thread_|.
+
+  // The thread's id once it was started.
+  PlatformThreadId id_;
+  mutable base::Lock id_lock_;  // Protects |id_|.
 
   // The thread's message loop.  Valid only while the thread is alive.  Set
   // by the created thread.