Remove parallel sweeping mode, it's no longer used

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index 9df3e6f1446280a9ad3564e4db24de9bce7d5b22..e888a2df0f34bbf8a7452101678bdc48bb5ce3f4 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -205,10 +205,8 @@ static void VerifyEvacuation(NewSpace* space) {
 
 
 static void VerifyEvacuation(PagedSpace* space) {
-  // TODO(hpayer): Bring back VerifyEvacuation for parallel-concurrently
-  // swept pages.
-  if ((FLAG_concurrent_sweeping || FLAG_parallel_sweeping) &&
-      !space->is_iterable()) return;
+  // TODO(hpayer): Bring back VerifyEvacuation for concurrently swept pages.
+  if (FLAG_concurrent_sweeping && !space->is_iterable()) return;
   PageIterator it(space);
 
   while (it.has_next()) {
@@ -4147,8 +4145,7 @@ void MarkCompactCollector::SweepSpace(PagedSpace* space, SweeperType sweeper) {
     }
 
     switch (sweeper) {
-      case CONCURRENT_CONSERVATIVE:
-      case PARALLEL_CONSERVATIVE: {
+      case CONCURRENT_CONSERVATIVE: {
         if (!parallel_sweeping_active) {
           if (FLAG_gc_verbose) {
             PrintF("Sweeping 0x%" V8PRIxPTR " conservatively.\n",
@@ -4209,9 +4206,6 @@ void MarkCompactCollector::SweepSpaces() {
   state_ = SWEEP_SPACES;
 #endif
   SweeperType how_to_sweep = CONCURRENT_CONSERVATIVE;
-  if (FLAG_parallel_sweeping) how_to_sweep = PARALLEL_CONSERVATIVE;
-  if (FLAG_concurrent_sweeping) how_to_sweep = CONCURRENT_CONSERVATIVE;
-
   if (sweep_precisely_) how_to_sweep = PRECISE;
 
   MoveEvacuationCandidatesToEndOfPagesList();
@@ -4227,14 +4221,9 @@ void MarkCompactCollector::SweepSpaces() {
       SweepSpace(heap()->old_data_space(), how_to_sweep);
     }
 
-    if (how_to_sweep == PARALLEL_CONSERVATIVE ||
-        how_to_sweep == CONCURRENT_CONSERVATIVE) {
+    if (how_to_sweep == CONCURRENT_CONSERVATIVE) {
       StartSweeperThreads();
     }
-
-    if (how_to_sweep == PARALLEL_CONSERVATIVE) {
-      EnsureSweepingCompleted();
-    }
   }
   RemoveDeadInvalidatedCode();