Wait for sweeper threads in incremental marking step when sweeper threads are done sweeping.

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index 8263b5d9d77b01e2769f36fc1e85d8ca8db7e902..1a1105386b7f9746929e6e50d98a50273b471ad2 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -608,6 +608,22 @@ void MarkCompactCollector::WaitUntilSweepingCompleted() {
 }
 
 
+bool MarkCompactCollector::IsSweepingCompleted() {
+  for (int i = 0; i < isolate()->num_sweeper_threads(); i++) {
+    if (!isolate()->sweeper_threads()[i]->SweepingCompleted()) {
+      return false;
+    }
+  }
+  if (FLAG_job_based_sweeping) {
+    if (!pending_sweeper_jobs_semaphore_.WaitFor(TimeDelta::FromSeconds(0))) {
+      return false;
+    }
+    pending_sweeper_jobs_semaphore_.Signal();
+  }
+  return true;
+}
+
+
 void MarkCompactCollector::RefillFreeList(PagedSpace* space) {
   FreeList* free_list;