Again at https://build.chromium.org/p/chromium.fyi/builders/Fuchsia/builds/8684

[00008.522] 02491.02874> [ RUN      ] SharedBufferTest.CreateAndPassReadOnlyBuffer
[00008.522] 02491.02874> [3:56802096:0811/214126.012337:8182145:WARNING:test_suite.cc(235)] Test launcher output path /tmp/.org.chromium.Chromium.JBBEMh/test_results.xml exists. Not adding test launcher result printer.
[00008.522] 02491.02874> [3:853957424:0811/214126.256869:8426629:FATAL:mojo_test_base.cc(144)] Check failed: MOJO_RESULT_OK == ReadMessageRaw(MessagePipeHandle(mp), &bytes, &handles, MOJO_READ_MESSAGE_FLAG_NONE) (0 vs. 9)
----- start symbolized stack
#00: StackTrace at /b/c/builder/linux/src/out/Release/../../base/debug/stack_trace_fuchsia.cc:169
#01: std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::endl<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&) at /b/c/builder/linux/src/out/Release/../../buildtools/third_party/libc++/trunk/include/ostream:1001
      (inlined by) std::__1::basic_ostream<char, std::__1::char_traits<char> >::operator<<(std::__1::basic_ostream<char, std::__1::char_traits<char> >& (*)(std::__1::basic_ostream<char, std::__1::char_traits<char> >&)) at /b/c/builder/linux/src/out/Release/../../buildtools/third_party/libc++/trunk/include/ostream:195
      (inlined by) ~LogMessage at /b/c/builder/linux/src/out/Release/../../base/logging.cc:554
#02: std::__1::vector<mojo::ScopedHandleBase<mojo::Handle>, std::__1::allocator<mojo::ScopedHandleBase<mojo::Handle> > >::size() const at /b/c/builder/linux/src/out/Release/../../buildtools/third_party/libc++/trunk/include/vector:638
      (inlined by) mojo::edk::test::MojoTestBase::ReadMessageWithHandles(unsigned int, unsigned int*, unsigned int) at /b/c/builder/linux/src/out/Release/../../mojo/edk/test/mojo_test_base.cc:145
#03: mojo::edk::test::MojoTestBase::ReadMessage(unsigned int) at /b/c/builder/linux/src/out/Release/../../mojo/edk/test/mojo_test_base.cc:175
#04: std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::__get_short_size() const at /b/c/builder/linux/src/out/Release/../../buildtools/third_party/libc++/trunk/include/string:1276
      (inlined by) std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::size() const at /b/c/builder/linux/src/out/Release/../../buildtools/third_party/libc++/trunk/include/string:892
      (inlined by) bool std::__1::operator==<char, std::__1::char_traits<char>, std::__1::allocator<char> >(char const*, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) at /b/c/builder/linux/src/out/Release/../../buildtools/third_party/libc++/trunk/include/string:3570
      (inlined by) testing::AssertionResult testing::internal::CmpHelperEQ<char [3], std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >(char const*, char const*, char const (&) [3], std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) at /b/c/builder/linux/src/out/Release/../../third_party/googletest/src/googletest/include/gtest/gtest.h:1392
      (inlined by) testing::AssertionResult testing::internal::EqHelper<false>::Compare<char [3], std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >(char const*, char const*, char const (&) [3], std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) at /b/c/builder/linux/src/out/Release/../../third_party/googletest/src/googletest/include/gtest/gtest.h:1421
      (inlined by) operator() at /b/c/builder/linux/src/out/Release/../../mojo/edk/system/shared_buffer_unittest.cc:271
      (inlined by) int mojo::edk::test::MojoTestBase::RunTestClientAndGetExitCode<mojo::edk::(anonymous namespace)::SharedBufferTest_CreateAndPassReadOnlyBuffer_Test::TestBody()::$_6>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, mojo::edk::(anonymous namespace)::SharedBufferTest_CreateAndPassReadOnlyBuffer_Test::TestBody()::$_6) at /b/c/builder/linux/src/out/Release/../../mojo/edk/test/mojo_test_base.h:78
      (inlined by) void mojo::edk::test::MojoTestBase::RunTestClient<mojo::edk::(anonymous namespace)::SharedBufferTest_CreateAndPassReadOnlyBuffer_Test::TestBody()::$_6>(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, mojo::edk::(anonymous namespace)::SharedBufferTest_CreateAndPassReadOnlyBuffer_Test::TestBody()::$_6) at /b/c/builder/linux/src/out/Release/../../mojo/edk/test/mojo_test_base.h:71
      (inlined by) mojo::edk::(anonymous namespace)::SharedBufferTest_CreateAndPassReadOnlyBuffer_Test::TestBody() at /b/c/builder/linux/src/out/Release/../../mojo/edk/system/shared_buffer_unittest.cc:261
#05: testing::internal::UnitTestImpl::os_stack_trace_getter() at /b/c/builder/linux/src/out/Release/../../third_party/googletest/src/googletest/src/gtest.cc:4918
      (inlined by) testing::Test::Run() at /b/c/builder/linux/src/out/Release/../../third_party/googletest/src/googletest/src/gtest.cc:2478
#06: testing::internal::UnitTestImpl::os_stack_trace_getter() at /b/c/builder/linux/src/out/Release/../../third_party/googletest/src/googletest/src/gtest.cc:4918
      (inlined by) testing::TestInfo::Run() at /b/c/builder/linux/src/out/Release/../../third_party/googletest/src/googletest/src/gtest.cc:2657
#07: testing::TestCase::Run() at /b/c/builder/linux/src/out/Release/../../third_party/googletest/src/googletest/src/gtest.cc:2770
#08: testing::internal::UnitTestImpl::RunAllTests() at /b/c/builder/linux/src/out/Release/../../third_party/googletest/src/googletest/src/gtest.cc:4647
#09: testing::UnitTest::Run() at /b/c/builder/linux/src/out/Release/../../third_party/googletest/src/googletest/src/gtest.cc:4256
#10: RUN_ALL_TESTS() at /b/c/builder/linux/src/out/Release/../../third_party/googletest/src/googletest/include/gtest/gtest.h:2237
      (inlined by) base::TestSuite::Run() at /b/c/builder/linux/src/out/Release/../../base/test/test_suite.cc:270
#11: base::Callback<int (), (base::internal::CopyMode)1, (base::internal::RepeatMode)1>::Run() const & at /b/c/builder/linux/src/out/Release/../../base/callback.h:80
      (inlined by) base::(anonymous namespace)::LaunchUnitTestsInternal(base::Callback<int (), (base::internal::CopyMode)1, (base::internal::RepeatMode)1> const&, unsigned long, int, bool, base::Callback<void (), (base::internal::CopyMode)1, (base::internal::RepeatMode)1> const&) at /b/c/builder/linux/src/out/Release/../../base/test/launcher/unit_test_launcher.cc:216
#12: base::LaunchUnitTests(int, char**, base::Callback<int (), (base::internal::CopyMode)1, (base::internal::RepeatMode)1> const&) at /b/c/builder/linux/src/out/Release/../../base/test/launcher/unit_test_launcher.cc:475
#13: main at /b/c/builder/linux/src/out/Release/../../mojo/edk/test/run_all_unittests.cc:46
#14: mojo_system_unittests+0x1c22e
----- end symbolized stack
[00008.522] 02491.02874>
[00008.523] 02491.02874> [31/203] SharedBufferTest.CreateAndPassReadOnlyBuffer (CRASHED)

And again at

https://build.chromium.org/p/chromium.fyi/builders/Fuchsia/builds/8721

and

https://build.chromium.org/p/chromium.fyi/builders/Fuchsia/builds/8729

ReadMessageRaw() is returning MOJO_RESULT_FAILED_PRECONDITION, which basically indicates:

1. Something went wrong with Message serialization (see https://cs.chromium.org/chromium/src/mojo/edk/system/core.cc?type=cs&l=590) during the read operation.
2. The peer already closed the message pipe (see https://cs.chromium.org/chromium/src/mojo/edk/system/message_pipe_dispatcher.cc?type=cs&l=188).

However, we don't seem to be getting mojo_system_unittests failures any more, so closing this out.