DevTools: make sure Network.requestWillBeSent is emitted on time for sync xhrs

Network.requestWillBeSent event wasn't flushed for redirects that happen
inside sync XHRs.

R=caseq

Change-Id: I342188fb71e3efff05516b7add5ed1b3d4e9879f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1586346
Commit-Queue: Andrey Lushnikov <lushnikov@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654750}
5 files changed