[heap] Start concurrent marking simultaneously with incremental marking.

src/heap/heap.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HEAP_HEAP_H_
 #define V8_HEAP_HEAP_H_
 
 #include <cmath>
 #include <map>
 
@@ skipping 1221 matching lines @@
 
   void FinalizeIncrementalMarkingIfComplete(GarbageCollectionReason gc_reason);
 
   bool TryFinalizeIdleIncrementalMarking(double idle_time_in_ms,
                                          GarbageCollectionReason gc_reason);
 
   void RegisterReservationsForBlackAllocation(Reservation* reservations);
 
   IncrementalMarking* incremental_marking() { return incremental_marking_; }
 
+  // ===========================================================================
+  // Concurrent marking API. ===================================================
+  // ===========================================================================
+
+  ConcurrentMarking* concurrent_marking() { return concurrent_marking_; }
+
   // The runtime uses this function to notify potentially unsafe object layout
   // changes that require special synchronization with the concurrent marker.
   // A layout change is unsafe if
   // - it removes a tagged in-object field.
   // - it replaces a tagged in-objects field with an untagged in-object field.
   void NotifyObjectLayoutChange(HeapObject* object,
                                 const DisallowHeapAllocation&);
 #ifdef VERIFY_HEAP
   // This function checks that either
   // - the map transition is safe,
@@ skipping 1369 matching lines @@
   friend class LargeObjectSpace;
   friend class NewSpace;
   friend class PagedSpace;
   DISALLOW_COPY_AND_ASSIGN(AllocationObserver);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_HEAP_H_