make debug mode ~20% faster on linux

base/threading/thread_checker_impl.cc

Index: base/threading/thread_checker_impl.cc
diff --git a/base/threading/thread_checker_impl.cc b/base/threading/thread_checker_impl.cc
index 985433e5f1154a5e11bc18b58d70e1a89aa00d40..eb87bae772cbbf9be35ccddad88ed886b1b1052a 100644
--- a/base/threading/thread_checker_impl.cc
+++ b/base/threading/thread_checker_impl.cc
@@ -7,7 +7,7 @@
 namespace base {
 
 ThreadCheckerImpl::ThreadCheckerImpl()
-    : valid_thread_id_(kInvalidThreadId) {
+    : valid_thread_id_() {
   EnsureThreadIdAssigned();
 }
 
@@ -16,19 +16,19 @@ ThreadCheckerImpl::~ThreadCheckerImpl() {}
 bool ThreadCheckerImpl::CalledOnValidThread() const {
   EnsureThreadIdAssigned();
   AutoLock auto_lock(lock_);
-  return valid_thread_id_ == PlatformThread::CurrentId();
+  return valid_thread_id_ == PlatformThread::CurrentRef();
 }
 
 void ThreadCheckerImpl::DetachFromThread() {
   AutoLock auto_lock(lock_);
-  valid_thread_id_ = kInvalidThreadId;
+  valid_thread_id_ = PlatformThreadRef();
 }
 
 void ThreadCheckerImpl::EnsureThreadIdAssigned() const {
   AutoLock auto_lock(lock_);
-  if (valid_thread_id_ != kInvalidThreadId)
-    return;
-  valid_thread_id_ = PlatformThread::CurrentId();
+  if (valid_thread_id_.is_null()) {
+    valid_thread_id_ = PlatformThread::CurrentRef();
+  }
 }
 
 }  // namespace base