[heap] Add concurrency-safe refilling to compaction spaces

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 da75d6c983c983518e88893d6ed520db9ff76080..3a3f8e2a4542c2b3739ecd8dce507926dd0a1279 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -457,10 +457,19 @@ class MarkCompactCollector {
   // size of the maximum continuous freed memory chunk.
   int SweepInParallel(Page* page, PagedSpace* space);
 
+  // Ensures that sweeping is finished.
+  //
+  // Note: Can only be called safely from main thread.
   void EnsureSweepingCompleted();
 
   void SweepOrWaitUntilSweepingCompleted(Page* page);
 
+  // Help out in sweeping the corresponding space and refill memory that has
+  // been regained.
+  //
+  // Note: Thread-safe.
+  void SweepAndRefill(CompactionSpace* space);
+
   // If sweeper threads are not active this method will return true. If
   // this is a latency issue we should be smarter here. Otherwise, it will
   // return true if the sweeper threads are done processing the pages.