GitLab

GCD API was used to make sure that completion callbacks are called
during the app shutdown. Calling completion handler is required by
WKWebView, otherwise web view throws an exception. This CL uses
WebThread::PostTask instead of GCD behind feature flag. This will allow
to run an experiment to see if using WebThread::PostTask leads to crashes
during app shutdown.

WebThread::PostTask is preferable for testing, because there is no
good way to wait until GCD tasks are completed in a unit test.

Bug: 853774
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Ie9eefa7f7cef0c7432a2f733086fc5d630d8a969
Reviewed-on: https://chromium-review.googlesource.com/1113182Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570028}