Document that tests should avoid using bare SWPs.

base/threading/sequenced_worker_pool.h

Index: base/threading/sequenced_worker_pool.h
diff --git a/base/threading/sequenced_worker_pool.h b/base/threading/sequenced_worker_pool.h
index 1bd275b206d4b5b20ecece5da227ad1488beced0..d3c85e23ae4690217ab764867738a02d3e1ad1cc 100644
--- a/base/threading/sequenced_worker_pool.h
+++ b/base/threading/sequenced_worker_pool.h
@@ -69,6 +69,9 @@ class SequencedTaskRunner;
 //
 // Note that SequencedWorkerPool is RefCountedThreadSafe (inherited
 // from TaskRunner).
+//
+// Test-only code should wrap this in a base::SequencedWorkerPoolOwner to avoid
+// memory leaks. See http://crbug.com/273800
 class BASE_EXPORT SequencedWorkerPool : public TaskRunner {
  public:
   // Defines what should happen to a task posted to the worker pool on