[heap] Don't clear black areas in Heap::AllocateFillerObject.

BUG=chromium:630386

Review-Url: https://codereview.chromium.org/2258083002
Cr-Commit-Position: refs/heads/master@{#38750}

src/heap/heap.cc

@@ -2132,7 +2132,8 @@ AllocationResult Heap::AllocateFillerObject(int size, bool double_align,
   MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
   DCHECK(chunk->owner()->identity() == space);
 #endif
-  CreateFillerObjectAt(obj->address(), size, ClearRecordedSlots::kNo);
+  CreateFillerObjectAt(obj->address(), size, ClearRecordedSlots::kNo,
+                       ClearBlackArea::kNo);
   return obj;
 }