[heap] Black allocation.

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 0c4c57d6488b1aeea462c491d54ea8d14031dbf9..9df79746ee64a12eea471412115f5bf70303303b 100644
--- a/src/heap/mark-compact-inl.h
+++ b/src/heap/mark-compact-inl.h
@@ -143,10 +143,21 @@ template <LiveObjectIterationMode T>
 HeapObject* LiveObjectIterator<T>::Next() {
   while (!it_.Done()) {
     HeapObject* object = nullptr;
+    if (T == kGreyObjectsOnBlackPage) {
+      // Black objects will have most of the mark bits set to 1. If we invert
+      // the mark bits, grey objects will be left but the mark bit is moved by
+      // one position. We can just substract one word from the found location
+      // to obtain the grey object.
+      current_cell_ = ~current_cell_;
+    }
     while (current_cell_ != 0) {
       uint32_t trailing_zeros = base::bits::CountTrailingZeros32(current_cell_);
       Address addr = cell_base_ + trailing_zeros * kPointerSize;
 
+      if (T == kGreyObjectsOnBlackPage) {
+        addr -= kPointerSize;
+      }
+
       // Clear the first bit of the found object..
       current_cell_ &= ~(1u << trailing_zeros);
 
@@ -168,6 +179,8 @@ HeapObject* LiveObjectIterator<T>::Next() {
         object = HeapObject::FromAddress(addr);
       } else if (T == kAllLiveObjects) {
         object = HeapObject::FromAddress(addr);
+      } else if (T == kGreyObjectsOnBlackPage) {
+        object = HeapObject::FromAddress(addr);
       }
       // Clear the second bit of the found object.
       current_cell_ &= ~second_bit_index;