Introduce --job-based-sweeping flag and use individual jobs for sweeping if set

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index bc24b71a678b0c6b3d24ba57ed35c6c9b46c4ec4..6267a8896d123d0d861a57f83ab755bce933047f 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -1671,6 +1671,10 @@ void Isolate::Deinit() {
     delete[] sweeper_thread_;
     sweeper_thread_ = NULL;
 
+    if (FLAG_job_based_sweeping &&
+        heap_.mark_compact_collector()->IsConcurrentSweepingInProgress()) {
+      heap_.mark_compact_collector()->WaitUntilSweepingCompleted();
+    }
 
     if (FLAG_hydrogen_stats) GetHStatistics()->Print();
 
@@ -2010,7 +2014,10 @@ bool Isolate::Init(Deserializer* des) {
     max_available_threads_ = Max(Min(CPU::NumberOfProcessorsOnline(), 4), 1);
   }
 
-  num_sweeper_threads_ = SweeperThread::NumberOfThreads(max_available_threads_);
+  if (!FLAG_job_based_sweeping) {
+    num_sweeper_threads_ =
+        SweeperThread::NumberOfThreads(max_available_threads_);
+  }
 
   if (FLAG_trace_hydrogen || FLAG_trace_hydrogen_stubs) {
     PrintF("Concurrent recompilation has been disabled for tracing.\n");