Revert of [heap] Remove live weak cells from weak cell list when finalizing...

Revert of [heap] Remove live weak cells from weak cell list when finalizing incremental marking. (patchset #3 id:40001 of https://codereview.chromium.org/1474303002/ )

Reason for revert:
Still investigating bad canary.

Original issue's description:
> [heap] Remove live weak cells from weak cell list when finalizing incremental marking.
>
> BUG=chromium:548562
> LOG=n
>
> Committed: https://crrev.com/6190c608c8f3ced0f00ff53965e115b78646cecd
> Cr-Commit-Position: refs/heads/master@{#32372}

TBR=ulan@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:548562

Review URL: https://codereview.chromium.org/1481383004

Cr-Commit-Position: refs/heads/master@{#32459}

src/heap/incremental-marking.cc

@@ -647,44 +647,6 @@ void IncrementalMarking::MarkObjectGroups() {
 }
 
 
-void IncrementalMarking::ProcessWeakCells() {
-  DCHECK(FLAG_finalize_marking_incrementally);
-  DCHECK(!finalize_marking_completed_);
-  DCHECK(IsMarking());
-
-  Object* weak_cell_obj = heap()->encountered_weak_cells();
-  Object* weak_cell_head = Smi::FromInt(0);
-  WeakCell* prev_weak_cell_obj = NULL;
-  while (weak_cell_obj != Smi::FromInt(0)) {
-    WeakCell* weak_cell = reinterpret_cast<WeakCell*>(weak_cell_obj);
-    // We do not insert cleared weak cells into the list, so the value
-    // cannot be a Smi here.
-    HeapObject* value = HeapObject::cast(weak_cell->value());
-    // Remove weak cells with live objects from the list, they do not need
-    // clearing.
-    if (MarkCompactCollector::IsMarked(value)) {
-      // Record slot, if value is pointing to an evacuation candidate.
-      Object** slot = HeapObject::RawField(weak_cell, WeakCell::kValueOffset);
-      heap_->mark_compact_collector()->RecordSlot(weak_cell, slot, *slot);
-      // Remove entry somewhere after top.
-      if (prev_weak_cell_obj != NULL) {
-        prev_weak_cell_obj->set_next(weak_cell->next());
-      }
-      weak_cell_obj = weak_cell->next();
-      weak_cell->clear_next(heap());
-    } else {
-      if (weak_cell_head == Smi::FromInt(0)) {
-        weak_cell_head = weak_cell;
-      }
-      prev_weak_cell_obj = weak_cell;
-      weak_cell_obj = weak_cell->next();
-    }
-  }
-  // Top may have changed.
-  heap()->set_encountered_weak_cells(weak_cell_head);
-}
-
-
 void IncrementalMarking::FinalizeIncrementally() {
   DCHECK(FLAG_finalize_marking_incrementally);
   DCHECK(!finalize_marking_completed_);
@@ -697,11 +659,8 @@ void IncrementalMarking::FinalizeIncrementally() {
   // objects to reduce the marking load in the final pause.
   // 1) We scan and mark the roots again to find all changes to the root set.
   // 2) We mark the object groups.
-  // 3) Remove weak cell with live values from the list of weak cells, they
-  // do not need processing during GC.
   MarkRoots();
   MarkObjectGroups();
-  ProcessWeakCells();
 
   int marking_progress =
       abs(old_marking_deque_top -

src/heap/incremental-marking.h

@@ -240,7 +240,6 @@ class IncrementalMarking {
 
   void MarkRoots();
   void MarkObjectGroups();
-  void ProcessWeakCells();
 
   void ActivateIncrementalWriteBarrier(PagedSpace* space);
   static void ActivateIncrementalWriteBarrier(NewSpace* space);