Network Service: Fix some LoginPromptBrowserTest by adding |do_not_prompt_for_login_| flag for URLLoader

This CL fixes some LoginPromptBrowserTest by adding a
|do_not_prompt_for_login_| flag for URLLoader. It is similar to what
ResourceLoader::OnAuthRequired() does.

Bug: 783990
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_mojo
Change-Id: I86d72fcf64429a3d78231ce55fc1bb07359c7caa
Reviewed-on: https://chromium-review.googlesource.com/1015742
Commit-Queue: Jun Cai <juncai@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555653}

• content/browser/loader/resource_dispatcher_host_impl.cc[diff]
• content/renderer/loader/web_url_loader_impl.cc[diff]
• services/network/url_loader.cc[diff]
• services/network/url_loader.h[diff]
• services/network/url_loader_unittest.cc[diff]
• services/test/BUILD.gn[diff]
• services/test/data/has_favicon.html[Added - diff]
• testing/buildbot/filters/mojo.fyi.network_browser_tests.filter[diff]
• third_party/WebKit/LayoutTests/flag-specific/enable-features=NetworkService/http/tests/inspector-protocol/network/xhr-interception-auth-fail-expected.txt[Added - diff]