Wait for sweeper threads when a scan on scavenge page is not swept.

src/mark-compact.h

Index: src/mark-compact.h
diff --git a/src/mark-compact.h b/src/mark-compact.h
index 1145badba6b9429f5d47bf8cc217c53ce4285ea6..638076f0b07ac6f63f0e8f5f0390c2e8daa4561a 100644
--- a/src/mark-compact.h
+++ b/src/mark-compact.h
@@ -658,9 +658,14 @@ class MarkCompactCollector {
   // Concurrent and parallel sweeping support. If required_freed_bytes was set
   // to a value larger than 0, then sweeping returns after a block of at least
   // required_freed_bytes was freed. If required_freed_bytes was set to zero
-  // then the whole given space is swept.
+  // then the whole given space is swept. It returns the size of the maximum
+  // continuous freed memory chunk.
   int SweepInParallel(PagedSpace* space, int required_freed_bytes);
 
+  // Sweeps a given page concurrently to the sweeper threads. It returns the
+  // size of the maximum continuous freed memory chunk.
+  int SweepInParallel(Page* page, PagedSpace* space);
+
   void EnsureSweepingCompleted();
 
   // If sweeper threads are not active this method will return true. If