[tsan] Avoid modifying flags back and forth for each microtask queue test

... but do it once for the whole group of tests instead.

Bug: v8:8929
Change-Id: I4c92a4cc29f8cf8a1011a563fe41972844c59972
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1511476Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60122}

test/unittests/background-compile-task-unittest.cc

@@ -36,11 +36,11 @@ class BackgroundCompileTaskTest : public TestWithNativeContext {
   static void SetUpTestCase() {
     CHECK_NULL(save_flags_);
     save_flags_ = new SaveFlags();
-    TestWithNativeContext ::SetUpTestCase();
+    TestWithNativeContext::SetUpTestCase();
   }
 
   static void TearDownTestCase() {
-    TestWithNativeContext ::TearDownTestCase();
+    TestWithNativeContext::TearDownTestCase();
     CHECK_NOT_NULL(save_flags_);
     delete save_flags_;
     save_flags_ = nullptr;

test/unittests/compiler-dispatcher/compiler-dispatcher-unittest.cc

@@ -59,11 +59,11 @@ class CompilerDispatcherTest : public TestWithNativeContext {
 
   static void SetUpTestCase() {
     CompilerDispatcherTestFlags::SetFlagsForTest();
-    TestWithNativeContext ::SetUpTestCase();
+    TestWithNativeContext::SetUpTestCase();
   }
 
   static void TearDownTestCase() {
-    TestWithNativeContext ::TearDownTestCase();
+    TestWithNativeContext::TearDownTestCase();
     CompilerDispatcherTestFlags::RestoreFlags();
   }
 

test/unittests/microtask-queue-unittest.cc

@@ -32,17 +32,33 @@ void RunStdFunction(void* data) {
 template <typename TMixin>
 class WithFinalizationGroupMixin : public TMixin {
  public:
-  WithFinalizationGroupMixin() {
+  WithFinalizationGroupMixin() = default;
+  ~WithFinalizationGroupMixin() override = default;
+
+  static void SetUpTestCase() {
+    CHECK_NULL(save_flags_);
+    save_flags_ = new SaveFlags();
     FLAG_harmony_weak_refs = true;
     FLAG_expose_gc = true;
+    TMixin::SetUpTestCase();
+  }
+
+  static void TearDownTestCase() {
+    TMixin::TearDownTestCase();
+    CHECK_NOT_NULL(save_flags_);
+    delete save_flags_;
+    save_flags_ = nullptr;
   }
 
  private:
-  SaveFlags save_flags_;
+  static SaveFlags* save_flags_;
 
   DISALLOW_COPY_AND_ASSIGN(WithFinalizationGroupMixin);
 };
 
+template <typename TMixin>
+SaveFlags* WithFinalizationGroupMixin<TMixin>::save_flags_ = nullptr;
+
 using TestWithNativeContextAndFinalizationGroup =  //
     WithInternalIsolateMixin<                      //
         WithContextMixin<                          //