Disable Signed Exchange when Network Service is enabled

This patch (temporarily) disables Signed Exchange when Network Service
feature is enabled, since cert and CT verification we currently use (via
URLRequestContext) is not wired up in the Network Service code path.

If Network Service feature is enabled, WebPackageLoader will fail with
ERR_INVALID_SIGNED_EXCHANGE and warning message will be shown on devtools.

WebPackageRequestHandlerBrowserTest tests this behavior. Layout tests
with network service are disabled for now.

Bug: 849935
Change-Id: Ic72f9af4d68f55d8557ea0c631020ed871408a70
Reviewed-on: https://chromium-review.googlesource.com/1088270
Reviewed-by: Tsuyoshi Horo <[email protected]>
Reviewed-by: Kouhei Ueno <[email protected]>
Reviewed-by: Kinuko Yasuda <[email protected]>
Commit-Queue: Kunihiko Sakamoto <[email protected]>
Cr-Commit-Position: refs/heads/master@{#564835}
5 files changed