[heap] Use cancelable tasks during compaction.

src/heap/mark-compact.h

Index: src/heap/mark-compact.h
diff --git a/src/heap/mark-compact.h b/src/heap/mark-compact.h
index fb562bf6876104ba42101902387b571c30bdc619..a729aed108532673cd74b6298eb87935fea7dc02 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -718,8 +718,6 @@ class MarkCompactCollector {
   // The number of parallel compaction tasks, including the main thread.
   int NumberOfParallelCompactionTasks();
 
-  void WaitUntilCompactionCompleted();
-
   void EvacuateNewSpaceAndCandidates();
 
   void VisitLiveObjects(Page* page, ObjectVisitor* visitor);
@@ -797,9 +795,6 @@ class MarkCompactCollector {
   // Semaphore used to synchronize compaction tasks.
   base::Semaphore pending_compaction_tasks_semaphore_;
 
-  // Number of active compaction tasks (including main thread).
-  intptr_t concurrent_compaction_tasks_active_;
-
   friend class Heap;
 };