[heap] Refactor incremental marking step.

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 1048 matching lines @@
   // incremental steps.
   void StartIdleIncrementalMarking();
 
   // Starts incremental marking assuming incremental marking is currently
   // stopped.
   void StartIncrementalMarking(int gc_flags = kNoGCFlags,
                                const GCCallbackFlags gc_callback_flags =
                                    GCCallbackFlags::kNoGCCallbackFlags,
                                const char* reason = nullptr);
 
+  void StartIncrementalMarkingIfNeeded(int gc_flags = kNoGCFlags,
+                                       const GCCallbackFlags gc_callback_flags =
+                                           GCCallbackFlags::kNoGCCallbackFlags,
+                                       const char* reason = nullptr);
+
   void FinalizeIncrementalMarkingIfComplete(const char* comment);
 
   bool TryFinalizeIdleIncrementalMarking(double idle_time_in_ms);
 
   void RegisterReservationsForBlackAllocation(Reservation* reservations);
 
   IncrementalMarking* incremental_marking() { return incremental_marking_; }
 
   // ===========================================================================
   // Embedder heap tracer support. =============================================
@@ skipping 1440 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_