Add cross-reference documentation about the forgotten RefCountedDeleteOnSequence.

content/public/browser/browser_thread.h

Index: content/public/browser/browser_thread.h
diff --git a/content/public/browser/browser_thread.h b/content/public/browser/browser_thread.h
index 77b2f00a821c2dae59765ae09712731cbc33e095..47bcbfc8eb40334e3f578a03bfcc262c416218c5 100644
--- a/content/public/browser/browser_thread.h
+++ b/content/public/browser/browser_thread.h
@@ -316,7 +316,8 @@ class CONTENT_EXPORT BrowserThread {
   // std::unique_ptr<Foo, BrowserThread::DeleteOnIOThread> ptr;
   //
   // Note: when migrating BrowserThreads to TaskScheduler based
-  // SequencedTaskRunners these map to base::OnTaskRunnerDeleter.
+  // SequencedTaskRunners these map to base::OnTaskRunnerDeleter and
+  // base::RefCountedDeleteOnSequence.
   struct DeleteOnUIThread : public DeleteOnThread<UI> { };
   struct DeleteOnIOThread : public DeleteOnThread<IO> { };
   struct DeleteOnFileThread : public DeleteOnThread<FILE> { };