[heap] Avoid overzealous inclusion of heap internal headers.

src/heap/mark-compact-inl.h

Index: src/heap/mark-compact-inl.h
diff --git a/src/heap/mark-compact-inl.h b/src/heap/mark-compact-inl.h
index c78ae650df9ffea23cd42705abdc4d60f75fb09c..0acbe07662c93a21dc47c61c3260e296f6fa95b8 100644
--- a/src/heap/mark-compact-inl.h
+++ b/src/heap/mark-compact-inl.h
@@ -13,12 +13,6 @@ namespace v8 {
 namespace internal {
 
 
-MarkBit Marking::MarkBitFrom(Address addr) {
-  MemoryChunk* p = MemoryChunk::FromAddress(addr);
-  return p->markbits()->MarkBitFromIndex(p->AddressToMarkbitIndex(addr));
-}
-
-
 void MarkCompactCollector::SetFlags(int flags) {
   reduce_memory_footprint_ = ((flags & Heap::kReduceMemoryFootprintMask) != 0);
   abort_incremental_marking_ =