[heap] Add --stress-incremental-marking flag.

test/cctest/test-unboxed-doubles.cc

Index: test/cctest/test-unboxed-doubles.cc
diff --git a/test/cctest/test-unboxed-doubles.cc b/test/cctest/test-unboxed-doubles.cc
index 7911412c2dc22dd4948853bf34f8707e9f4e6dc2..972ba26c60b78f6acdbe83603bf000484266c0a2 100644
--- a/test/cctest/test-unboxed-doubles.cc
+++ b/test/cctest/test-unboxed-doubles.cc
@@ -1109,6 +1109,7 @@ TEST(DoScavenge) {
 
 TEST(DoScavengeWithIncrementalWriteBarrier) {
   if (FLAG_never_compact || !FLAG_incremental_marking) return;
+  FLAG_stress_incremental_marking = false;
   CcTest::InitializeVM();
   v8::HandleScope scope(CcTest::isolate());
   Isolate* isolate = CcTest::i_isolate();
@@ -1457,6 +1458,7 @@ static void TestIncrementalWriteBarrier(Handle<Map> map, Handle<Map> new_map,
                                         int double_descriptor,
                                         bool check_tagged_value = true) {
   if (FLAG_never_compact || !FLAG_incremental_marking) return;
+  FLAG_stress_incremental_marking = false;
   FLAG_manual_evacuation_candidates_selection = true;
   Isolate* isolate = CcTest::i_isolate();
   Factory* factory = isolate->factory();
@@ -1539,6 +1541,7 @@ enum OldToWriteBarrierKind {
 };
 static void TestWriteBarrierObjectShiftFieldsRight(
     OldToWriteBarrierKind write_barrier_kind) {
+  FLAG_stress_incremental_marking = false;
   CcTest::InitializeVM();
   Isolate* isolate = CcTest::i_isolate();
   v8::HandleScope scope(CcTest::isolate());