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

base/threading/thread.cc

Index: base/threading/thread.cc
diff --git a/base/threading/thread.cc b/base/threading/thread.cc
index 7bff24232e2bf2d66fda4485a4246ebae2e98332..ad6133286434f1d57ae9089851b1bfaacccc3e9b 100644
--- a/base/threading/thread.cc
+++ b/base/threading/thread.cc
@@ -62,6 +62,8 @@ Thread::Thread(const std::string& name)
       stopping_(false),
       running_(false),
       thread_(0),
+      id_(kInvalidThreadId),
+      id_event_(true, false),
       message_loop_(nullptr),
       message_loop_timer_slack_(TIMER_SLACK_NONE),
       name_(name) {
@@ -87,6 +89,9 @@ bool Thread::StartWithOptions(const Options& options) {
       (options.message_loop_type == MessageLoop::TYPE_UI));
 #endif
 
+  id_event_.Reset();
+  id_ = kInvalidThreadId;
+
   SetThreadWasQuitProperly(false);
 
   MessageLoop::Type type = options.message_loop_type;
@@ -177,8 +182,9 @@ void Thread::StopSoon() {
 }
 
 PlatformThreadId Thread::thread_id() const {
-  AutoLock lock(thread_lock_);
-  return thread_.id();
+  base::ThreadRestrictions::ScopedAllowWait allow_wait;
+  id_event_.Wait();
+  return id_;
 }
 
 bool Thread::IsRunning() const {
@@ -211,6 +217,11 @@ bool Thread::GetThreadWasQuitProperly() {
 }
 
 void Thread::ThreadMain() {
+  // Make thread_id() available first since it could be called any place.
+  id_ = PlatformThread::CurrentId();
+  DCHECK_NE(kInvalidThreadId, id_);
+  id_event_.Signal();
+
   // Complete the initialization of our Thread object.
   PlatformThread::SetName(name_.c_str());
   ANNOTATE_THREAD_NAME(name_.c_str());  // Tell the name to race detector.
@@ -231,10 +242,6 @@ void Thread::ThreadMain() {
   }
 #endif
 
-  // Make sure the thread_id() returns current thread.
-  // (This internally acquires lock against PlatformThread::Create)
-  DCHECK_EQ(thread_id(), PlatformThread::CurrentId());
-
   // Let the thread do extra initialization.
   Init();