Enforce that mock host resolver isn't modified in a test body.

content/public/test/browser_test_base.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/public/test/browser_test_base.h"
 
 #include <stddef.h>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 363 matching lines @@
 
 void BrowserTestBase::InitializeNetworkProcess() {
   const testing::TestInfo* const test_info =
       testing::UnitTest::GetInstance()->current_test_info();
   bool network_service = base::CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kEnableNetworkService);
   // ProcessTransferAfterError is the only browser test which needs to modify
   // the host rules (when not using the network service).
   if (network_service ||
       std::string(test_info->name()) != "ProcessTransferAfterError") {
-    // TODO(jam): enable this once all access to host_resolver() is in
-    // SetUpOnMainThread or before. http://crbug.com/713847
-    // host_resolver()->DisableModifications();
+    host_resolver()->DisableModifications();
   }
 
   if (!network_service)
     return;
 
   net::RuleBasedHostResolverProc::RuleList rules = host_resolver()->GetRules();
   std::vector<mojom::RulePtr> mojo_rules;
   for (const auto& rule : rules) {
     // For now, this covers all the rules used in content's tests.
     // TODO(jam: expand this when we try to make browser_tests and
@@ skipping 12 matching lines @@
   if (mojo_rules.empty())
     return;
 
   mojom::NetworkServiceTestPtr network_service_test;
   ServiceManagerConnection::GetForProcess()->GetConnector()->BindInterface(
       mojom::kNetworkServiceName, &network_service_test);
   network_service_test->AddRules(std::move(mojo_rules));
 }
 
 }  // namespace content