Fuzzer: Enable PostToCreateThead for Linux.

Test disabled on Linux due to flakiness. However, it wasn't linked
to a relevant bug. Also, I run this for 2+ hours on a Linux
workstation and I got no failures. So, I am landing this unit test
again.

Bug: 875170
Change-Id: Ic6719945d85c0d0e707aa809cbbb18d10ed9bfb3
Reviewed-on: https://chromium-review.googlesource.com/1188320
Commit-Queue: Farah Charab <farahcharab@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586154}

third_party/blink/renderer/platform/scheduler/test/fuzzer/sequence_manager_fuzzer_processor_unittest.cc

@@ -1238,13 +1238,7 @@ TEST(SequenceManagerFuzzerProcessorTest, CreateThreadRecursively) {
   EXPECT_THAT(executed_actions, ContainerEq(expected_actions));
 }
 
-// Disabled since this test is flaky on Linux. https://crbug.com/875170.
-#if defined(OS_LINUX)
-#define MAYBE_PostTaskToCreateThread DISABLED_PostTaskToCreateThread
-#else
-#define MAYBE_PostTaskToCreateThread PostTaskToCreateThread
-#endif
-TEST(SequenceManagerFuzzerProcessorTest, MAYBE_PostTaskToCreateThread) {
+TEST(SequenceManagerFuzzerProcessorTest, PostTaskToCreateThread) {
   std::vector<std::vector<ActionForTest>> executed_actions;
   std::vector<std::vector<TaskForTest>> executed_tasks;