Add debugging code for crashes in network::ThrottlingController.

 * Check called on valid thread
 * Crash with a more specific callstack on use-after-free, or certain data corruptions

These checks are only run when network throttling is enabled through the Chrome DevTools, so won't have a performance impact in the common case.

Bug: 960874
Change-Id: I45bfecc6755a60afaf369fc53c464a3bbd36d9fc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1620818
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661549}
2 files changed