[Media Router] Conditionally enable mDNS on Windows.

chrome/browser/media/router/media_route_provider_util_win.cc

+// Copyright 2016 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 "chrome/browser/media/router/media_route_provider_util_win.h"
+
+#include "base/files/file_path.h"
+#include "base/location.h"
+#include "base/path_service.h"
+#include "chrome/installer/util/browser_distribution.h"
+#include "chrome/installer/util/firewall_manager_win.h"
+#include "content/public/browser/browser_thread.h"
+
+namespace media_router {
+
+namespace {
+
+void DoCanFirewallUseLocalPorts(const base::Callback<void(bool)>& callback) {
+  base::FilePath exe_path;

[mark a. foltz, 2016/03/29 00:48:20]

Add a DCHECK_CURRENTLY_ON(content::BrowserThread::FILE) at the top of the fn

+  bool can_use_local_ports = false;
+  if (base::PathService::Get(base::FILE_EXE, &exe_path)) {

[mark a. foltz, 2016/03/29 00:48:20]

If the firewall check fails to run at all, it might be good to have a way to
know that.

Consider having early returns after LOG(WARNING) if these preconditions fail
(base::PathService::Get, firewall_manager).

I don't know these implementations in detail; if it looks like these are very
rare/extremely broken situations, then maybe not worth it.

+    auto firewall_manager = installer::FirewallManager::Create(
+        BrowserDistribution::GetDistribution(), exe_path);
+    can_use_local_ports =
+        firewall_manager && firewall_manager->CanUseLocalPorts();
+  }
+  content::BrowserThread::PostTask(
+      content::BrowserThread::UI, FROM_HERE,
+      base::Bind(callback, can_use_local_ports));
+}
+
+}  // namespace
+
+void CanFirewallUseLocalPorts(const base::Callback<void(bool)>& callback) {
+  content::BrowserThread::PostTask(
+      content::BrowserThread::FILE, FROM_HERE,
+      base::Bind(&DoCanFirewallUseLocalPorts, callback));
+}
+
+}  // namespace media_router