[heap] Do not clear mark bits of left trimmed old object start.

test/cctest/heap/test-heap.cc

Index: test/cctest/heap/test-heap.cc
diff --git a/test/cctest/heap/test-heap.cc b/test/cctest/heap/test-heap.cc
index 3042ca8df88b094c6b87706634e8b24fbc5db7ba..459891be3bd5b0c9cdc7a1129c4a8f387e93beb7 100644
--- a/test/cctest/heap/test-heap.cc
+++ b/test/cctest/heap/test-heap.cc
@@ -6372,7 +6372,7 @@ TEST(ContinuousLeftTrimFixedArrayInBlackArea) {
     HeapObject* filler = HeapObject::FromAddress(previous->address());
     CHECK(filler->IsFiller());
     CHECK(Marking::IsBlack(ObjectMarking::MarkBitFrom(trimmed)));
-    CHECK(Marking::IsImpossible(ObjectMarking::MarkBitFrom(previous)));
+    CHECK(Marking::IsBlack(ObjectMarking::MarkBitFrom(previous)));
     previous = trimmed;
   }
 
@@ -6383,7 +6383,7 @@ TEST(ContinuousLeftTrimFixedArrayInBlackArea) {
       HeapObject* filler = HeapObject::FromAddress(previous->address());
       CHECK(filler->IsFiller());
       CHECK(Marking::IsBlack(ObjectMarking::MarkBitFrom(trimmed)));
-      CHECK(Marking::IsWhite(ObjectMarking::MarkBitFrom(previous)));
+      CHECK(Marking::IsBlack(ObjectMarking::MarkBitFrom(previous)));
       previous = trimmed;
     }
   }