These tests were just failing on the VM for a very long time.
Rewrite them into a simpler version that just tests conditional
importing rather than trying to do clever things with HttpRequest.
R=eernst@google.com
Change-Id: Iebb7f6210ae4f2215c9445695189533116ffb5b7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/338160
Commit-Queue: Slava Egorov <vegorov@google.com>
Reviewed-by: Erik Ernst <eernst@google.com>
