Waiting for sweeper threads is last resort in SlowAllocateRaw.

src/spaces.h

Index: src/spaces.h
diff --git a/src/spaces.h b/src/spaces.h
index fcf7a442011db54071a52ce40d26eec0a857dd3b..9127d2c1da9e45a058d5f3905843935d7e25a414 100644
--- a/src/spaces.h
+++ b/src/spaces.h
@@ -2007,8 +2007,11 @@ class PagedSpace : public Space {
   // address denoted by top in allocation_info_.
   inline HeapObject* AllocateLinearly(int size_in_bytes);
 
+  MUST_USE_RESULT HeapObject*
+      WaitForSweeperThreadsAndRetryAllocation(int size_in_bytes);
+
   // Slow path of AllocateRaw.  This function is space-dependent.
-  MUST_USE_RESULT virtual HeapObject* SlowAllocateRaw(int size_in_bytes);
+  MUST_USE_RESULT HeapObject* SlowAllocateRaw(int size_in_bytes);
 
   friend class PageIterator;
   friend class MarkCompactCollector;