Sync the browser test host resolver with the network process before a test runs.

content/public/test/test_host_resolver.cc

Index: content/public/test/test_host_resolver.cc
diff --git a/content/public/test/test_host_resolver.cc b/content/public/test/test_host_resolver.cc
new file mode 100644
index 0000000000000000000000000000000000000000..da2bfd00b974190f69462a79026b08ca79e93834
--- /dev/null
+++ b/content/public/test/test_host_resolver.cc
@@ -0,0 +1,77 @@
+// Copyright 2017 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/test_host_resolver.h"
+
+#include "base/macros.h"
+#include "base/message_loop/message_loop.h"
+#include "base/threading/thread.h"
+#include "content/browser/browser_thread_impl.h"
+#include "content/browser/notification_service_impl.h"
+#include "net/base/net_errors.h"
+#include "net/base/network_interfaces.h"
+#include "net/dns/mock_host_resolver.h"
+
+namespace content {
+
+namespace {
+// In many cases it may be not obvious that a test makes a real DNS lookup.
+// We generally don't want to rely on external DNS servers for our tests,
+// so this host resolver procedure catches external queries and returns a failed
+// lookup result.
+class LocalHostResolverProc : public net::HostResolverProc {
+ public:
+  LocalHostResolverProc() : HostResolverProc(NULL) {}
+
+  int Resolve(const std::string& host,
+              net::AddressFamily address_family,
+              net::HostResolverFlags host_resolver_flags,
+              net::AddressList* addrlist,
+              int* os_error) override {
+    const char* kLocalHostNames[] = {"localhost", "127.0.0.1", "::1"};
+    bool local = false;
+
+    if (host == net::GetHostName()) {
+      local = true;
+    } else {
+      for (size_t i = 0; i < arraysize(kLocalHostNames); i++)
+        if (host == kLocalHostNames[i]) {
+          local = true;
+          break;
+        }
+    }
+
+    // To avoid depending on external resources and to reduce (if not preclude)
+    // network interactions from tests, we simulate failure for non-local DNS
+    // queries, rather than perform them.
+    // If you really need to make an external DNS query, use
+    // net::RuleBasedHostResolverProc and its AllowDirectLookup method.
+    if (!local) {
+      DVLOG(1) << "To avoid external dependencies, simulating failure for "
+                  "external DNS lookup of "
+               << host;
+      return net::ERR_NOT_IMPLEMENTED;
+    }
+
+    return ResolveUsingPrevious(host, address_family, host_resolver_flags,
+                                addrlist, os_error);
+  }
+
+ private:
+  ~LocalHostResolverProc() override {}
+};
+}
+
+TestHostResolver::TestHostResolver()
+    : local_resolver_(new LocalHostResolverProc()),
+      rule_based_resolver_(
+          new net::RuleBasedHostResolverProc(local_resolver_.get())),
+      scoped_local_host_resolver_proc_(
+          new net::ScopedDefaultHostResolverProc(rule_based_resolver_.get())) {
+  rule_based_resolver_->AddSimulatedFailure("wpad");
+}
+
+TestHostResolver::~TestHostResolver() {}
+
+}  // namespace content