Disable WorkerThreadTest.TestTaskExecutedBeforeThreadDeletion on Linux

The test is flaky
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=blink_platform_unittests&tests=WorkerThreadTest.TestTaskExecutedBeforeThreadDeletion

Bug: 934088
Change-Id: I4d783da07af305a094d41f32383e16e98ca48f43
Reviewed-on: https://chromium-review.googlesource.com/c/1481310Reviewed-by: Christos Froussios <cfroussios@chromium.org>
Reviewed-by: Alex Clarke <alexclarke@chromium.org>
Auto-Submit: Christos Froussios <cfroussios@chromium.org>
Commit-Queue: Alex Clarke <alexclarke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634589}

third_party/blink/renderer/platform/scheduler/worker/worker_thread_unittest.cc

@@ -119,7 +119,12 @@ TEST_F(WorkerThreadTest, TestDefaultTask) {
   completion.Wait();
 }
 
-TEST_F(WorkerThreadTest, TestTaskExecutedBeforeThreadDeletion) {
+#if defined(OS_LINUX)
+#define MAYBE_TestTaskExecutedBeforeThreadDeletion DISABLED_TestTaskExecutedBeforeThreadDeletion
+#else
+#define MAYBE_TestTaskExecutedBeforeThreadDeletion TestTaskExecutedBeforeThreadDeletion
+#endif
+TEST_F(WorkerThreadTest, MAYBE_TestTaskExecutedBeforeThreadDeletion) {
   MockTask task;
   base::WaitableEvent completion(
       base::WaitableEvent::ResetPolicy::AUTOMATIC,