AXSystemCaretWinTest.TestCaretMSAAEvents is flaky.

Was introduced here:
https://chromium-review.googlesource.com/c/chromium/src/+/1236735

Example run:

https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Win10%20Tests%20x64/28240

 AXSystemCaretWinTest.TestCaretMSAAEvents
  ../../ui/views/accessibility/ax_system_caret_win_interactive_uitest.cc(321): error: Expected: (AccessibleObjectFromWindow( hwnd, static_cast<DWORD>(((LONG)0xFFFFFFF8)), IID_IAccessible, reinterpret_cast<void**>(caret_accessible.GetAddressOf()))) succeeds.
    Actual: 0x80004005 Unspecified error
  Stack trace:
  Backtrace:
  	testing::internal::UnitTestImpl::CurrentOsStackTraceExceptTop [0x00007FF7ABDC5F27+87]
  	testing::internal::AssertHelper::operator= [0x00007FF7ABDC5AAE+78]
  	views::AXSystemCaretWinTest_TestCaretMSAAEvents_Test::TestBody [0x00007FF7ABDB03AC+492]
  [3012:8336:1005/201557.303:32140250:FATAL:ax_system_caret_win_interactive_uitest.cc(159)] Check failed: S_OK == AccessibleObjectFromEvent( event_info.hwnd, event_info.obj_id, event_info.child_id, acc_obj.GetAddressOf(), child_variant.Receive()).
  Backtrace:
  	base::debug::StackTrace::StackTrace [0x00007FF7ADBDFA54+36]
  	logging::LogMessage::~LogMessage [0x00007FF7ADBF6C32+98]
  	views::AXSystemCaretWinTest_TestCaretMSAAEvents_Test::TestBody [0x00007FF7ABDB11BF+4095]
  	views::AXSystemCaretWinTest_TestCaretMSAAEvents_Test::TestBody [0x00007FF7ABDB0416+598]
  	testing::Test::Run [0x00007FF7ABDCA0B7+199]
  	testing::TestInfo::Run [0x00007FF7ABDCA9F9+217]
  	testing::TestCase::Run [0x00007FF7ABDCAF62+258]
  	testing::internal::UnitTestImpl::RunAllTests [0x00007FF7ABDD26FE+638]
  	testing::UnitTest::Run [0x00007FF7ABDD23C5+165]
  	base::TestSuite::Run [0x00007FF7ADBD6ED6+118]
  	InteractiveUITestSuiteRunner::RunTestSuite [0x00007FF7ABD06EE6+70]
  	content::LaunchTests [0x00007FF7ADA6F58A+410]
  	LaunchChromeTests [0x00007FF7ADA01D42+306]
  	main [0x00007FF7ABD06E44+116]
  	__scrt_common_main_seh [0x00007FF7B17B3C28+268] (f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:283)
  	BaseThreadInitThunk [0x00007FFA85F92774+20]
  	RtlUserThreadStart [0x00007FFA86280D51+33]

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d1bddb1ff49a16dd5c974de7a2f4518398c6d288

commit d1bddb1ff49a16dd5c974de7a2f4518398c6d288
Author: Aaron Leventhal <aleventhal@chromium.org>
Date: Tue Oct 09 01:44:23 2018

Disable flaky caret test

TBR=nektar@chromium.org

Bug:  891565 
Change-Id: I151ec8cdcc578d8650f67053d338dfe06d926bcf
Reviewed-on: https://chromium-review.googlesource.com/c/1270335
Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597768}
[modify] https://crrev.com/d1bddb1ff49a16dd5c974de7a2f4518398c6d288/ui/views/accessibility/ax_system_caret_win_interactive_uitest.cc