This CL is due the thread I have made on chromium-dev:...

base/thread_collision_warner.cc

+// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/thread_collision_warner.h"
+
+#include "base/atomicops.h"
+#include "base/logging.h"
+
+namespace base {
+
+void DCheckAsserter::warn() { DCHECK(false) << "Thread Collision"; }
+
+void ThreadCollisionWarner::EnterSelf() {
+  // If the active thread is 0 then I'll write the current thread ID
+  // if two or more threads arrive here only one will success to 
+  // write on valid_thread_id_ the current thread ID.
+
+  const int current_thread_id = PlatformThread::CurrentId();
+
+  if (subtle::NoBarrier_CompareAndSwap(&valid_thread_id_,
+                                       0,
+                                       current_thread_id) != 0) {
+
+    // Last chance! may be is the thread itself calling from a 
+    // critical section another critical section, need to check if
+    // valid_thread_id == current_thread_id.
+
+    if (subtle::NoBarrier_CompareAndSwap(&valid_thread_id_, 
+                                         current_thread_id,
+                                         valid_thread_id_) !=
+        current_thread_id ) {
+      // gotcha! a thread is trying to use the same class and that is
+      // not current thread.
+      asserter_->warn();
+    }
+  }
+
+  subtle::NoBarrier_AtomicIncrement(&counter_, 1);
+}
+
+void ThreadCollisionWarner::Enter() {
+
+  const int current_thread_id = PlatformThread::CurrentId();
+
+  if (subtle::NoBarrier_CompareAndSwap(&valid_thread_id_,
+                                       0,
+                                       current_thread_id) != 0) {
+    // gotcha! another thread is trying to use the same class.
+    asserter_->warn();
+  }
+
+  subtle::NoBarrier_AtomicIncrement(&counter_, 1);
+}
+
+void ThreadCollisionWarner::Leave() {
+  if (subtle::Barrier_AtomicIncrement(&counter_, -1) == 0 ) {
+    subtle::NoBarrier_Store(&valid_thread_id_, 0);
+  }
+}
+
+}  // namespace base