Wait for sweeper threads only if we have to.

src/spaces.cc

Index: src/spaces.cc
diff --git a/src/spaces.cc b/src/spaces.cc
index 300d19e0d6dbd6cb78bfd32e47e19b643a0356dd..e34bcbd2a0e135f2a6f0f1dfb2218f30e3824b32 100644
--- a/src/spaces.cc
+++ b/src/spaces.cc
@@ -2546,8 +2546,8 @@ void PagedSpace::PrepareForMarkCompact() {
 
 
 intptr_t PagedSpace::SizeOfObjects() {
-  ASSERT(heap()->mark_compact_collector()->IsConcurrentSweepingInProgress() ||
-         (unswept_free_bytes_ == 0));
+  ASSERT(heap()->mark_compact_collector()->
+      IsConcurrentSweepingInProgress(this) || (unswept_free_bytes_ == 0));
   return Size() - unswept_free_bytes_ - (limit() - top());
 }
 
@@ -2582,7 +2582,7 @@ HeapObject* PagedSpace::WaitForSweeperThreadsAndRetryAllocation(
   MarkCompactCollector* collector = heap()->mark_compact_collector();
 
   // If sweeper threads are still running, wait for them.
-  if (collector->IsConcurrentSweepingInProgress()) {
+  if (collector->IsConcurrentSweepingInProgress(this)) {
     collector->WaitUntilSweepingCompleted();
 
     // After waiting for the sweeper threads, there may be new free-list
@@ -2598,7 +2598,7 @@ HeapObject* PagedSpace::SlowAllocateRaw(int size_in_bytes) {
 
   // If sweeper threads are active, try to re-fill the free-lists.
   MarkCompactCollector* collector = heap()->mark_compact_collector();
-  if (collector->IsConcurrentSweepingInProgress()) {
+  if (collector->IsConcurrentSweepingInProgress(this)) {
     collector->RefillFreeList(this);
 
     // Retry the free list allocation.