Suspected CL: https://chromium-review.googlesource.com/c/chromium/src/+/1171568

Also looks like different PPAPI test flaking on Win 7:

https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Win%207%20Tests%20x64%20%281%29/42258

With an unknown set of flakes across OSes I'm going to land a revert.

And for the record, the original failure is:

[ RUN      ] PPAPINaClGLibcTest.UDPSocket_Broadcast
[4507:6403:0822/133832.696492:WARNING:notification_platform_bridge_mac.mm(510)] AlertNotificationService: XPC connection invalidated.
[4540,1967632384:13:38:34.238340] Native Client module will be loaded at base address 0x0000550100000000
[4507:90115:0822/133834.391473:WARNING:embedded_test_server.cc(238)] Request not handled. Returning 404: /favicon.ico
[4507:775:0822/133834.834858:INFO:CONSOLE(176)] "BroadcastForceAsync finished in 0.004 seconds.", source: http://127.0.0.1:50722/test_case.html?mode=nacl_glibc&testcase=UDPSocket_Broadcast, (176)
[4507:775:0822/133834.839739:INFO:CONSOLE(176)] "Broadcast finished in 0.012 seconds.", source: http://127.0.0.1:50722/test_case.html?mode=nacl_glibc&testcase=UDPSocket_Broadcast, (176)
[4507:775:0822/133834.844217:INFO:CONSOLE(176)] "BroadcastBlocking finished in 0.004 seconds.", source: http://127.0.0.1:50722/test_case.html?mode=nacl_glibc&testcase=UDPSocket_Broadcast, (176)
[4507:775:0822/133834.848948:INFO:CONSOLE(176)] "BroadcastBackground finished in 0.004 seconds.", source: http://127.0.0.1:50722/test_case.html?mode=nacl_glibc&testcase=UDPSocket_Broadcast, (176)
../../chrome/test/ppapi/ppapi_test.cc:251: Failure
Expected equality of these values:
  "PASS"
  handler.message().c_str()
    Which is: "BroadcastForceAsync FAIL: Failure in ../../ppapi/tests/test_udp_socket.cc(273): Failure in ../../ppapi/tests/test_udp_socket.cc(151): Failed ASSERT_EQ(PP_OK, callback.result()) Left: (0) Right: (-108), Broadcast FAIL: Failure in ../../ppapi/tests/test_udp_socket.cc(273): Failure in ../../ppapi/tests/test_udp_socket.cc(151): Failed ASSERT_EQ(PP_OK, callback.result()) Left: (0) Right: (-108), BroadcastBlocking FAIL: Failure in ../../ppapi/tests/test_udp_socket.cc(273): Failure in ../../ppapi/tests/test_udp_socket.cc(151): Failed ASSERT_EQ(PP_OK, callback.result()) Left: (0) Right: (-108), BroadcastBackground FAIL: Failure in ../../ppapi/tests/test_udp_socket.cc(273): Failure in ../../ppapi/tests/test_udp_socket.cc(151): Failed ASSERT_EQ(PP_OK, callback.result()) Left: (0) Right: (-108)"
Stack trace:
0   browser_tests                       0x00000001104ed60b testing::internal::UnitTestImpl::CurrentOsStackTraceExceptTop(int) + 91
1   browser_tests                       0x00000001104ecfd9 testing::internal::AssertHelper::operator=(testing::Message const&) const + 89
2   browser_tests                       0x0000000112631f9e PPAPITestBase::RunTestURL(GURL const&) + 590
3   browser_tests                       0x0000000112632126 PPAPITestBase::RunTestViaHTTP(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) + 214
4   browser_tests                       0x000000010fa6fcff PPAPINaClGLibcTest_UDPSocket_Broadcast_Test::RunTestOnMainThread() + 79
5   browser_tests                       0x0000000112bcf49b content::BrowserTestBase::ProxyRunTestOnMainThreadLoop() + 491
6   browser_tests                       0x000000011269ff07 ChromeBrowserMainParts::PreMainMessageLoopRunImpl() + 4375
7   browser_tests                       0x000000011269ecee ChromeBrowserMainParts::PreMainMessageLoopRun() + 62
8   browser_tests                       0x000000011117a193 content::BrowserMainLoop::PreMainMessageLoopRun() + 67
9   browser_tests                       0x00000001115843c7 content::StartupTaskRunner::RunAllTasksNow() + 39
10  browser_tests                       0x00000001111788c8 content::BrowserMainLoop::CreateStartupTasks() + 712
11  browser_tests                       0x000000011117c6b0 content::BrowserMainRunnerImpl::Initialize(content::MainFunctionParams const&) + 96
12  browser_tests                       0x00000001111769e4 content::BrowserMain(content::MainFunctionParams const&) + 180
13  browser_tests                       0x00000001124d0690 content::ContentMainRunnerImpl::Run(bool) + 592
14  browser_tests                       0x00000001145a60b1 service_manager::Main(service_manager::MainParams const&) + 2849
15  browser_tests                       0x00000001124cf894 content::ContentMain(content::ContentMainParams const&) + 68
16  browser_tests                       0x0000000112bcf0c9 content::BrowserTestBase::SetUp() + 2697
17  browser_tests                       0x0000000112628873 InProcessBrowserTest::SetUp() + 723
[4507:775:0822/133835.143710:WARNING:pref_notifier_impl.cc(23)] Pref observer found at shutdown.
[4507:775:0822/133835.143851:WARNING:pref_notifier_impl.cc(23)] Pref observer found at shutdown.
[  FAILED  ] PPAPINaClGLibcTest.UDPSocket_Broadcast, where TypeParam =  and GetParam() =  (2611 ms)

-108 is ERR_ADDRESS_INVALID.

Oops, that's a pepper error, so -108 is actually PP_ERROR_ADDRESS_IN_USE.  SOCKET_OPTION_ADDRESS_REUSE does look like it's being correctly set, strangely.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/80c224c08e567070336c4762f8a56d405c134929

commit 80c224c08e567070336c4762f8a56d405c134929
Author: Matt Menke <mmenke@chromium.org>
Date: Mon Aug 27 23:44:45 2018

Make PepperUdpSocketMessageFilter use NetworkService UDP API.

This CL moves all of the logic over to the UI thread, to keep things
relatively simple and minimize thread hops, since that's where core
network service objects live.

It also fixes a pre-existing bug in the PPAPI UDP code, where read
errors that occur when there's no pending read are converted into
0-byte read successes.

This is a reland of https://chromium-review.googlesource.com/1171568,
which was reverted due to tests failing on OSX when broadcast was set
only after calling Bind, due to the Bind call failing. The new CL
uses a new UDPSocketOption to allow broadcast before calling Bind on
the underlying socket.

TBR=jam@chromium.org, rhalvati@chromium.org

Bug:  848078 ,  876824 
Change-Id: I0e31a357eb4b80bb78bae32f2a3ea3ce331256ec
Cq-Include-Trybots: luci.chromium.try:linux_mojo
Reviewed-on: https://chromium-review.googlesource.com/1190407
Reviewed-by: Matt Menke <mmenke@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586497}
[modify] https://crrev.com/80c224c08e567070336c4762f8a56d405c134929/chrome/test/ppapi/ppapi_browsertest.cc
[modify] https://crrev.com/80c224c08e567070336c4762f8a56d405c134929/content/browser/renderer_host/pepper/pepper_udp_socket_message_filter.cc
[modify] https://crrev.com/80c224c08e567070336c4762f8a56d405c134929/content/browser/renderer_host/pepper/pepper_udp_socket_message_filter.h
[modify] https://crrev.com/80c224c08e567070336c4762f8a56d405c134929/content/public/test/ppapi_test_utils.cc
[modify] https://crrev.com/80c224c08e567070336c4762f8a56d405c134929/content/public/test/ppapi_test_utils.h
[modify] https://crrev.com/80c224c08e567070336c4762f8a56d405c134929/ppapi/host/resource_message_filter.cc
[modify] https://crrev.com/80c224c08e567070336c4762f8a56d405c134929/ppapi/host/resource_message_filter.h
[modify] https://crrev.com/80c224c08e567070336c4762f8a56d405c134929/ppapi/proxy/udp_socket_filter.cc
[modify] https://crrev.com/80c224c08e567070336c4762f8a56d405c134929/ppapi/tests/test_udp_socket.cc
[modify] https://crrev.com/80c224c08e567070336c4762f8a56d405c134929/ppapi/tests/test_udp_socket.h
[modify] https://crrev.com/80c224c08e567070336c4762f8a56d405c134929/tools/traffic_annotation/summary/annotations.xml