Revert "Fix NetworkContextConfigurationBrowserTest.DnsCacheIsolation flake."

This reverts commit 1dd7e2a7.

Reason for revert: STill flaky.  Reverting both CLs.
NOTRY=true

Original change's description:
> Fix NetworkContextConfigurationBrowserTest.DnsCacheIsolation flake.
> 
> The test makes sure that HostCache entries aren't shared between
> NetworkContexts. To do this, it does a DNS lookup in one NetworkContext,
> which succeeds, and then cache-only DNS lookups in other NetworkContexts,
> which should fail. At the end of the test, it does a cache-only lookup
> in the first NetworkContext, which should succeed. It's generally best
> to do this at the end of the test, since it makes sure that entries
> aren't only usable once, or somesuch. Unfortunately, sometimes the
> DNS cache entry is timing out before the last lookup. To fix that,
> this CL moves the final cache-only lookup to be right after the
> initial lookup that populates the cache.
> 
> This does mean the test can still flakily pass, however, flaky successes
> are more tolerable than flaky failures, and the test currently passes
> often enough, even with the flake, that I think we can live with it.
> 
> Bug: 1043084
> Change-Id: Ibdcf77e7775943e18c21a9ddd2cd3d5bf127c248
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2008058
> Commit-Queue: Matt Menke <mmenke@chromium.org>
> Reviewed-by: Eric Orth <ericorth@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#733036}

TBR=mmenke@chromium.org,ericorth@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1043084
Change-Id: Ia4bffaad8793e7f660807c39d8e0cdfa95d8766b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2012080Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#733564}

chrome/browser/net/network_context_configuration_browsertest.cc

@@ -1137,26 +1137,8 @@ IN_PROC_BROWSER_TEST_P(NetworkContextConfigurationBrowserTest,
   EXPECT_EQ(kAddress,
             result.resolved_addresses.value()[0].ToStringWithoutPort());
 
-  // Do a cache-only lookup using the original network context, which should
-  // return the same result it initially did. This is done immediately after the
-  // lookup, as a race mitigation to minimize the chance of the cache entry
-  // expiring before this check.
-  network::mojom::ResolveHostParametersPtr params =
-      network::mojom::ResolveHostParameters::New();
-  // Cache only lookup.
-  params->source = net::HostResolverSource::LOCAL_ONLY;
-  result = network::BlockingDnsLookup(network_context(), host_port_pair,
-                                      std::move(params), network_isolation_key);
-  EXPECT_EQ(net::OK, result.error);
-  ASSERT_TRUE(result.resolved_addresses.has_value());
-  ASSERT_EQ(1u, result.resolved_addresses->size());
-  EXPECT_EQ(kAddress,
-            result.resolved_addresses.value()[0].ToStringWithoutPort());
-
   // Make a cache-only request for the same hostname, for each other network
-  // context, and make sure no result is returned. It's possible for the entry
-  // to expire during this test run, so on regression, this step may flakily
-  // pass.
+  // context, and make sure no result is returned.
   ForEachOtherContext(
       base::BindLambdaForTesting([&](NetworkContextType network_context_type) {
         network::mojom::ResolveHostParametersPtr params =
@@ -1168,6 +1150,20 @@ IN_PROC_BROWSER_TEST_P(NetworkContextConfigurationBrowserTest,
             host_port_pair, std::move(params), network_isolation_key);
         EXPECT_EQ(net::ERR_DNS_CACHE_MISS, result.error);
       }));
+
+  // Do a cache-only lookup using the original network context, which should
+  // return the same result it initially did.
+  network::mojom::ResolveHostParametersPtr params =
+      network::mojom::ResolveHostParameters::New();
+  // Cache only lookup.
+  params->source = net::HostResolverSource::LOCAL_ONLY;
+  result = network::BlockingDnsLookup(network_context(), host_port_pair,
+                                      std::move(params), network_isolation_key);
+  EXPECT_EQ(net::OK, result.error);
+  ASSERT_TRUE(result.resolved_addresses.has_value());
+  ASSERT_EQ(1u, result.resolved_addresses->size());
+  EXPECT_EQ(kAddress,
+            result.resolved_addresses.value()[0].ToStringWithoutPort());
 }
 
 // Visits a URL with an HSTS header, and makes sure it is respected.