dbus: Rewrite ObjectProxy::CallMethodWithErrorCallback's comment

To make it clear which callback can get a nullptr when.

BUG=None

Review-Url: https://codereview.chromium.org/2299853002
Cr-Commit-Position: refs/heads/master@{#415890}


CrOS-Libchrome-Original-Commit: fd6b5515d45ca8559708fa1479dd762ad7c67225
1 file changed
tree: d28ccb63fffb6fe01d89b1b10cab95b255e765de
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/