Make ThreadChecker::CalledOnValidThread() return true when called from the same task.

base/threading/thread_checker_impl.h

Index: base/threading/thread_checker_impl.h
diff --git a/base/threading/thread_checker_impl.h b/base/threading/thread_checker_impl.h
index 3e46316bc4e713fad2c0b84502339bc4b3a64904..13193d129932de0939f2c61bf76c3aa1ed8e8ea3 100644
--- a/base/threading/thread_checker_impl.h
+++ b/base/threading/thread_checker_impl.h
@@ -42,6 +42,14 @@ class BASE_EXPORT ThreadCheckerImpl {
   // Thread on which CalledOnValidThread() may return true.
   mutable PlatformThreadRef thread_id_;
 
+  // TaskToken for which CalledOnValidThread() always returns true. This allows
+  // CalledOnValidThread() to return true when called multiple times from the
+  // same task, even if it's not running in a single-threaded context itself
+  // (allowing usage of ThreadChecker/NonThreadSafe objects on the stack in the
+  // scope of one-off tasks). Note: CalledOnValidThread() may return true even
+  // if the current TaskToken is not equal to this.
+  mutable TaskToken task_token_;
+
   // SequenceToken for which CalledOnValidThread() may return true. Used to
   // ensure that CalledOnValidThread() doesn't return true for TaskScheduler
   // tasks that happen to run on the same thread but weren't posted to the same