Make NetworkContextConfigurationBrowserTest work when network service is enabled by default

NetworkContextConfigurationBrowserTest currently enables the network
service for the /1 tests, and leaves it in its default state for /0. If
the network service is enabled by default, leaving it in its default
state will result in it being enabled when it shouldn't.

This doesn't fix broken or flaky tests, just makes them behave as
intended.

Bug: 927293
Change-Id: Icda641679b42cba1c81061c00f82e35cf8a88500
Reviewed-on: https://chromium-review.googlesource.com/c/1457479
Auto-Submit: Robbie McElrath <rmcelrath@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630109}

chrome/browser/net/network_context_configuration_browsertest.cc

@@ -187,6 +187,8 @@ class NetworkContextConfigurationBrowserTest
   void SetUpInProcessBrowserTestFixture() override {
     if (GetParam().network_service_state != NetworkServiceState::kDisabled)
       feature_list_.InitAndEnableFeature(network::features::kNetworkService);
+    else
+      feature_list_.InitAndDisableFeature(network::features::kNetworkService);
   }
 
   void SetUpOnMainThread() override {