[heap] Minor MC: Implement page moving

src/heap/spaces.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HEAP_SPACES_H_
 #define V8_HEAP_SPACES_H_
 
 #include <list>
 #include <memory>
 #include <unordered_set>
@@ skipping 271 matching lines @@
     //   has been aborted and needs special handling by the sweeper.
     COMPACTION_WAS_ABORTED = 1u << 15,
 
     // |COMPACTION_WAS_ABORTED_FOR_TESTING|: During stress testing evacuation
     // on pages is sometimes aborted. The flag is used to avoid repeatedly
     // triggering on the same page.
     COMPACTION_WAS_ABORTED_FOR_TESTING = 1u << 16,
 
     // |ANCHOR|: Flag is set if page is an anchor.
     ANCHOR = 1u << 17,
+
+    // |SWEEP_TO_ITERATE|: The page requires sweeping using external markbits
+    // to iterate the page.
+    SWEEP_TO_ITERATE = 1u << 18,
   };
   typedef base::Flags<Flag, uintptr_t> Flags;
 
   static const int kPointersToHereAreInterestingMask =
       POINTERS_TO_HERE_ARE_INTERESTING;
 
   static const int kPointersFromHereAreInterestingMask =
       POINTERS_FROM_HERE_ARE_INTERESTING;
 
   static const int kEvacuationCandidateMask = EVACUATION_CANDIDATE;
@@ skipping 2666 matching lines @@
   PageIterator old_iterator_;
   PageIterator code_iterator_;
   PageIterator map_iterator_;
   LargePageIterator lo_iterator_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_SPACES_H_