First pass callbacks are required to reset the handle before entering
the second callback.

Make this a CHECK and properly document what is required to fix when
hitting this assertion.

Change-Id: I13c6b0342fca16544cec01620ac74a87c290b87d
Reviewed-on: https://chromium-review.googlesource.com/975609
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52169}