Use idle task to perform incremental marking steps.

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 1278 matching lines @@
   // deadline_ins_ms is not reached. step_size_in_bytes can be 0 to compute
   // an estimate increment. Returns the remaining time that cannot be used
   // for incremental marking anymore because a single step would exceed the
   // deadline.
   double AdvanceIncrementalMarking(
       intptr_t step_size_in_bytes, double deadline_in_ms,
       IncrementalMarking::StepActions step_actions);
 
   void FinalizeIncrementalMarkingIfComplete(const char* comment);
 
+  bool TryFinalizeIdleIncrementalMarking(double idle_time_in_ms);
+
   IncrementalMarking* incremental_marking() { return &incremental_marking_; }
 
   // ===========================================================================
   // External string table API. ================================================
   // ===========================================================================
 
   // Registers an external string.
   inline void RegisterExternalString(String* string);
 
   // Finalizes an external string by deleting the associated external
@@ skipping 1437 matching lines @@
   DisallowHeapAllocation no_allocation;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_HEAP_H_