There is a flakey use after free in FileManagerFileWatcherTest.WatchLocalFile on the CrOS ASan trybot.

==1781==ERROR: AddressSanitizer: stack-use-after-return on address 0x7f33892051d0 at pc 0x7f3391eea76e bp 0x7fffb4c464a0 sp 0x7fffb4c46498
READ of size 1 at 0x7f33892051d0 thread T0
    #0 0x7f3391eea76d in __is_long buildtools/third_party/libc++/trunk/include/string:1224:39
    #1 0x7f3391eea76d in capacity buildtools/third_party/libc++/trunk/include/string:896
    #2 0x7f3391eea76d in std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::assign(char const*, unsigned long) buildtools/third_party/libc++/trunk/include/string:1981
    #3 0x7f3391eea4f5 in std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::operator=(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&) buildtools/third_party/libc++/trunk/include/string:2045:9
    #4 0x10db1c0d in base::FilePath::operator=(base::FilePath const&) base/files/file_path.cc:190:9
    #5 0x5f06554 in void google_apis::test_util::internal::CopyResultCallback<base::FilePath, bool>(base::FilePath*, bool*, google_apis::test_util::internal::CopyResultCallbackHelper<base::FilePath>::InType, google_apis::test_util::internal::CopyResultCallbackHelper<bool>::InType) google_apis/drive/test_util.h:190:9
    #6 0x5f061ce in Run base/callback.h:64:12
    #7 0x5f061ce in void base::internal::FunctorTraits<base::OnceCallback<void (base::FilePath const&, bool)>, void>::Invoke<base::OnceCallback<void (base::FilePath const&, bool)>, base::FilePath, bool>(base::OnceCallback<void (base::FilePath const&, bool)>&&, base::FilePath&&, bool&&) base/bind_internal.h:238
    #8 0x1fb50a2b in Run base/callback.h:64:12
    #9 0x1fb50a2b in google_apis::test_util::RunAndQuit(base::RunLoop*, base::OnceCallback<void ()>) google_apis/drive/test_util.cc:52
    #10 0x5d714ae in Invoke<base::RunLoop *const &, base::OnceCallback<void ()> > base/bind_internal.h:149:12
    #11 0x5d714ae in MakeItSo<void (*const &)(base::RunLoop *, base::OnceCallback<void ()>), base::RunLoop *const &, base::OnceCallback<void ()> > base/bind_internal.h:277
    #12 0x5d714ae in RunImpl<void (*const &)(base::RunLoop *, base::OnceCallback<void ()>), const std::__1::tuple<base::RunLoop *> &, 0> base/bind_internal.h:349
    #13 0x5d714ae in base::internal::Invoker<base::internal::BindState<void (*)(base::RunLoop*, base::OnceCallback<void ()>), base::RunLoop*>, void (base::OnceCallback<void ()>)>::Run(base::internal::BindStateBase*, base::OnceCallback<void ()>&&) base/bind_internal.h:331
    #14 0x5f05a45 in Run base/callback.h:64:12
    #15 0x5f05a45 in google_apis::internal::ComposedCallback<void (base::FilePath const&, bool)>::Run(base::OnceCallback<void (base::OnceCallback<void ()>)>, base::OnceCallback<void (base::FilePath const&, bool)>, base::FilePath const&, bool) google_apis/drive/task_util.h:27
    #16 0x5f05c45 in Invoke<const base::RepeatingCallback<void (base::OnceCallback<void ()>)> &, const base::RepeatingCallback<void (const base::FilePath &, bool)> &, const base::FilePath &, bool> base/bind_internal.h:149:12
    #17 0x5f05c45 in MakeItSo<void (*const &)(base::OnceCallback<void (base::OnceCallback<void ()>)>, base::OnceCallback<void (const base::FilePath &, bool)>, const base::FilePath &, bool), const base::RepeatingCallback<void (base::OnceCallback<void ()>)> &, const base::RepeatingCallback<void (const base::FilePath &, bool)> &, const base::FilePath &, bool> base/bind_internal.h:277
    #18 0x5f05c45 in RunImpl<void (*const &)(base::OnceCallback<void (base::OnceCallback<void ()>)>, base::OnceCallback<void (const base::FilePath &, bool)>, const base::FilePath &, bool), const std::__1::tuple<base::RepeatingCallback<void (base::OnceCallback<void ()>)>, base::RepeatingCallback<void (const base::FilePath &, bool)> > &, 0, 1> base/bind_internal.h:349
    #19 0x5f05c45 in base::internal::Invoker<base::internal::BindState<void (*)(base::OnceCallback<void (base::OnceCallback<void ()>)>, base::OnceCallback<void (base::FilePath const&, bool)>, base::FilePath const&, bool), base::RepeatingCallback<void (base::OnceCallback<void ()>)>, base::RepeatingCallback<void (base::FilePath const&, bool)> >, void (base::FilePath const&, bool)>::Run(base::internal::BindStateBase*, base::FilePath const&, bool&&) base/bind_internal.h:331
    #20 0x5f061ce in Run base/callback.h:64:12
    #21 0x5f061ce in void base::internal::FunctorTraits<base::OnceCallback<void (base::FilePath const&, bool)>, void>::Invoke<base::OnceCallback<void (base::FilePath const&, bool)>, base::FilePath, bool>(base::OnceCallback<void (base::FilePath const&, bool)>&&, base::FilePath&&, bool&&) base/bind_internal.h:238
    #22 0x10da1372 in Run base/callback.h:64:12
    #23 0x10da1372 in base::debug::TaskAnnotator::RunTask(char const*, base::PendingTask*) base/debug/task_annotator.cc:65
    #24 0x10e1389a in base::MessageLoop::RunTask(base::PendingTask*) base/message_loop/message_loop.cc:406:19