Integrate concurrent sweeping with incremental marking.

src/incremental-marking.cc

Index: src/incremental-marking.cc
diff --git a/src/incremental-marking.cc b/src/incremental-marking.cc
index e2fca5b1a08059fea4eb213bbf65f7f1b6525581..658a34c9cd37e5150a51f5641c5168fe16ed5bf4 100644
--- a/src/incremental-marking.cc
+++ b/src/incremental-marking.cc
@@ -562,7 +562,6 @@ void IncrementalMarking::UncommitMarkingDeque() {
 
 
 void IncrementalMarking::Start() {
-  ASSERT(!heap_->mark_compact_collector()->IsConcurrentSweepingInProgress());
   if (FLAG_trace_incremental_marking) {
     PrintF("[IncrementalMarking] Start\n");
   }
@@ -901,7 +900,7 @@ void IncrementalMarking::Step(intptr_t allocated_bytes,
   }
 
   if (state_ == SWEEPING) {
-    if (heap_->AdvanceSweepers(static_cast<int>(bytes_to_process))) {
+    if (heap_->EnsureSweepersProgressed(static_cast<int>(bytes_to_process))) {
       bytes_scanned_ = 0;
       StartMarking(PREVENT_COMPACTION);
     }