XHR: Remove extra progress event dispatch when handling request error

The XMLHttpRequest spec (https://xhr.spec.whatwg.org/#request-error-steps) describes what steps to take in the event of a request error. Chrome currently dispatches a progress, an error, and a loadend event. Firefox and Edge 18.17763 follow the spec and only dispatch the error and loadend events.

Bug: 651750
Change-Id: I71512e7bb3dec9d706d36dc9f31bc7dc95de3bba
Reviewed-on: https://chromium-review.googlesource.com/c/1433114
Commit-Queue: Erik Anderson <Erik.Anderson@microsoft.com>
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625979}
8 files changed