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

test/cctest/heap/test-heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 6354 matching lines @@
 
   FixedArrayBase* previous = *array;
   FixedArrayBase* trimmed;
 
   // First trim in one word steps.
   for (int i = 0; i < 10; i++) {
     trimmed = heap->LeftTrimFixedArray(previous, 1);
     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;
   }
 
   // Then trim in two and three word steps.
   for (int i = 2; i <= 3; i++) {
     for (int j = 0; j < 10; j++) {
       trimmed = heap->LeftTrimFixedArray(previous, i);
       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;
     }
   }
 
   heap::GcAndSweep(heap, OLD_SPACE);
 }
 
 TEST(ContinuousRightTrimFixedArrayInBlackArea) {
   if (!i::FLAG_incremental_marking) return;
   FLAG_black_allocation = true;
@@ skipping 241 matching lines @@
   CHECK(!heap->code_space()->FirstPage()->Contains(code->address()));
 
   // Ensure it's not in large object space.
   MemoryChunk* chunk = MemoryChunk::FromAddress(code->address());
   CHECK(chunk->owner()->identity() != LO_SPACE);
   CHECK(chunk->NeverEvacuate());
 }
 
 }  // namespace internal
 }  // namespace v8