Elaborate on the CancelableCallback docs

base/cancelable_callback.h

 // Copyright (c) 2011 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.
 //
 // CancelableCallback is a wrapper around base::Callback that allows
 // cancellation of a callback. CancelableCallback takes a reference on the
 // wrapped callback until this object is destroyed or Reset()/Cancel() are
 // called.
 //
-// NOTE:
+// NOTES:
 //
 // Calling CancelableCallback::Cancel() brings the object back to its natural,
 // default-constructed state, i.e., CancelableCallback::callback() will return
 // a null callback.
 //
+// It is NOT allowed to call CancelableCallback::Cancel() or
+// CancelableCallback::Reset() from the wrapped callback.
+//
 // THREAD-SAFETY:
 //
-// CancelableCallback objects must be created on, posted to, cancelled on, and
+// CancelableCallback objects must be posted to, cancelled on, reset on, and
 // destroyed on the same thread.
 //
+// CancelableCallback objects are allowed to be constructed on a different

[emaxx, 2017/03/01 03:37:54]

Hmm, thinking more on this, this added comment is actually misleading: while
it's allowed to construct CancelableCallback on a different thread, it's not
allowed to _destruct_ them there (unless one can guarantee that there are no
callbacks currently posted anywhere, but that's probably not a typical use
case).

As it's becoming quite hard to explain this here, I'm starting to think that
this whole different-thread-corner-case should be simply disallowed, as before.
Any thoughts on this?

+// thread than on which they will be used later.
+//
 //
 // EXAMPLE USAGE:
 //
 // In the following example, the test is verifying that RunIntensiveTest()
 // Quit()s the message loop within 4 seconds. The cancelable callback is posted
 // to the message loop, the intensive test runs, the message loop is run,
 // then the callback is cancelled.
 //
 // RunLoop run_loop;
 //
@@ skipping 96 matching lines @@
   base::WeakPtrFactory<CancelableCallback<void(A...)>> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(CancelableCallback);
 };
 
 typedef CancelableCallback<void(void)> CancelableClosure;
 
 }  // namespace base
 
 #endif  // BASE_CANCELABLE_CALLBACK_H_