Reland of "heap] Fix Sweeper::IsSweepingCompleted"

src/heap/mark-compact.h

 // Copyright 2012 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_MARK_COMPACT_H_
 #define V8_HEAP_MARK_COMPACT_H_
 
 #include <deque>
 
 #include "src/base/bits.h"
@@ skipping 449 matching lines @@
 
     void PrepareToBeSweptPage(AllocationSpace space, Page* page);
 
     Heap* heap_;
     base::Semaphore pending_sweeper_tasks_semaphore_;
     base::Mutex mutex_;
     SweptList swept_list_[kAllocationSpaces];
     SweepingList sweeping_list_[kAllocationSpaces];
     bool sweeping_in_progress_;
     bool late_pages_;
-    int num_sweeping_tasks_;
+    base::AtomicNumber<intptr_t> num_sweeping_tasks_;
   };
 
   enum IterationMode {
     kKeepMarking,
     kClearMarkbits,
   };
 
   static void Initialize();
 
   void SetUp();
@@ skipping 409 matching lines @@
  private:
   MarkCompactCollector* collector_;
 };
 
 
 const char* AllocationSpaceName(AllocationSpace space);
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_MARK_COMPACT_H_