Allow main thread to contribute to the sweeping phase.

src/spaces.h

Index: src/spaces.h
diff --git a/src/spaces.h b/src/spaces.h
index 71b70546833824ea562cfdecf6b2f0336a5166b4..855359835293d05bf7523a7a5b187d96a4ec7cbb 100644
--- a/src/spaces.h
+++ b/src/spaces.h
@@ -2014,8 +2014,10 @@ 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);
+  // If sweeping is still in progress try to sweep unswept pages. If that is
+  // not successful, wait for the sweeper threads and re-try free-list
+  // allocation.
+  MUST_USE_RESULT HeapObject* EnsureSweepingProgress(int size_in_bytes);
 
   // Slow path of AllocateRaw.  This function is space-dependent.
   MUST_USE_RESULT HeapObject* SlowAllocateRaw(int size_in_bytes);