MediaRouterWebUIBrowserTest.OpenDialogWithMediaRouterAction is flakily timing out on the network_service_browser_tests step of the https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac10.12%20Tests bot.

Stack trace of the killed timed-out browser:

BrowserTestBase received signal: Terminated: 15. Backtrace:
0   browser_tests                       0x000000010c259f7f base::debug::StackTrace::StackTrace(unsigned long) + 31
1   browser_tests                       0x000000010c8e5835 content::(anonymous namespace)::DumpStackTraceSignalHandler(int) + 229
2   libsystem_platform.dylib            0x00007fff9402cb3a _sigtramp + 26
3   ???                                 0x0000000000000000 0x0 + 0
4   CoreFoundation                      0x00007fff7e695434 __CFRunLoopServiceMachPort + 212
5   CoreFoundation                      0x00007fff7e6948c1 __CFRunLoopRun + 1361
6   CoreFoundation                      0x00007fff7e694114 CFRunLoopRunSpecific + 420
7   HIToolbox                           0x00007fff7dbf4ebc RunCurrentEventLoopInMode + 240
8   HIToolbox                           0x00007fff7dbf4cf1 ReceiveNextEventCommon + 432
9   HIToolbox                           0x00007fff7dbf4b26 _BlockUntilNextEventMatchingListInModeWithFilter + 71
10  AppKit                              0x00007fff7c18da54 _DPSNextEvent + 1120
11  AppKit                              0x00007fff7c9097ee -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 2796
12  browser_tests                       0x000000010c329990 __71-[BrowserCrApplication nextEventMatchingMask:untilDate:inMode:dequeue:]_block_invoke + 64
13  browser_tests                       0x000000010c1942da base::mac::CallWithEHFrame(void () block_pointer) + 10
14  browser_tests                       0x000000010c3298c4 -[BrowserCrApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 164
15  AppKit                              0x00007fff7c1823db -[NSApplication run] + 926
16  browser_tests                       0x000000010c1a603c base::MessagePumpNSApplication::DoRun(base::MessagePump::Delegate*) + 348
17  browser_tests                       0x000000010c1a449f base::MessagePumpCFRunLoopBase::Run(base::MessagePump::Delegate*) + 127
18  browser_tests                       0x000000010c1d1285 base::RunLoop::Run() + 53
19  browser_tests                       0x000000010c91cbb1 content::MessageLoopRunner::Run() + 49
20  browser_tests                       0x0000000108e46b41 media_router::MediaRouterUIBrowserTest::OpenMediaRouterDialogAndWaitForNewWebContents() + 241
21  browser_tests                       0x0000000108e46823 media_router::MediaRouterWebUIBrowserTest_OpenDialogWithMediaRouterAction_Test::RunTestOnMainThread() + 547
22  browser_tests                       0x000000010c8e4e3b content::BrowserTestBase::ProxyRunTestOnMainThreadLoop() + 491
23  browser_tests                       0x000000010c32e579 ChromeBrowserMainParts::PreMainMessageLoopRunImpl() + 4313
24  browser_tests                       0x000000010c32d3dd ChromeBrowserMainParts::PreMainMessageLoopRun() + 45
25  browser_tests                       0x000000010a40c112 content::BrowserMainLoop::PreMainMessageLoopRun() + 50
26  browser_tests                       0x000000010a86f527 content::StartupTaskRunner::RunAllTasksNow() + 39
27  browser_tests                       0x000000010a40acbb content::BrowserMainLoop::CreateStartupTasks() + 683
28  browser_tests                       0x000000010a40e392 content::BrowserMainRunnerImpl::Initialize(content::MainFunctionParams const&) + 82
29  browser_tests                       0x000000010a409126 content::BrowserMain(content::MainFunctionParams const&) + 182
30  browser_tests                       0x000000010bdb4640 content::ContentMainRunnerImpl::RunServiceManager(content::MainFunctionParams&, bool) + 848
31  browser_tests                       0x000000010bdb42c4 content::ContentMainRunnerImpl::Run(bool) + 292
32  browser_tests                       0x000000010f120bc0 service_manager::Main(service_manager::MainParams const&) + 2352
33  browser_tests                       0x000000010bdb3484 content::ContentMain(content::ContentMainParams const&) + 68
34  browser_tests                       0x000000010c8e4a89 content::BrowserTestBase::SetUp() + 2809
35  browser_tests                       0x000000010c2a06e0 InProcessBrowserTest::SetUp() + 528
36  browser_tests                       0x00000001093124f0 testing::Test::Run() + 112
37  browser_tests                       0x000000010931342f testing::TestInfo::Run() + 463
38  browser_tests                       0x0000000109313ad7 testing::TestCase::Run() + 295
39  browser_tests                       0x0000000109320ae7 testing::internal::UnitTestImpl::RunAllTests() + 855
40  browser_tests                       0x000000010932076e testing::UnitTest::Run() + 142
41  browser_tests                       0x000000010c2c2906 base::TestSuite::Run() + 166
42  browser_tests                       0x000000010c1665cd ChromeTestSuiteRunner::RunTestSuite(int, char**) + 45
43  browser_tests                       0x000000010c916fa8 content::LaunchTests(content::TestLauncherDelegate*, unsigned long, int, char**) + 552
44  browser_tests                       0x000000010c166b7a LaunchChromeTests(unsigned long, content::TestLauncherDelegate*, int, char**) + 490
45  browser_tests                       0x000000010c16635e main + 94
46  libdyld.dylib                       0x00007fff93e1d235 start + 1
47  ???                                 0x000000000000000c 0x0 + 12