Fix typo in documentation of base/bind.h

Change-Id: Ib155760013ebf4e693d351d0478bb11eb0076f49
Reviewed-on: https://chromium-review.googlesource.com/c/1433659Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625836}

base/bind.h

@@ -29,7 +29,7 @@
 //
 //   // The first argument is bound at callback creation; the remaining
 //   // two must be passed when calling Run() on the callback object.
-//   base::OnceCallback<void(int, long)> cb = base::BindOnce(
+//   base::OnceCallback<long(int, long)> cb = base::BindOnce(
 //       [](short x, int y, long z) { return x * y * z; }, 42);
 //
 // When binding to a method, the receiver object must also be specified at