[heap] Add specific timer events for finalizing incremental GCs.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 996af169a0f003030e8191e776a193706124f4ff..715d9b22349031592e255950378c4ee5b5274a43 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -430,6 +430,7 @@ class GCIdleTimeHeapState;
 class GCTracer;
 class HeapObjectsFilter;
 class HeapStats;
+class HistogramTimer;
 class Isolate;
 class MemoryReducer;
 class ObjectStats;
@@ -1807,6 +1808,14 @@ class Heap {
   // objects that die later.
   void OverApproximateWeakClosure(const char* gc_reason);
 
+  // Returns the timer used for a given GC type.
+  // - GCScavenger: young generation GC
+  // - GCCompactor: full GC
+  // - GCFinalzeMC: finalization of incremental full GC
+  // - GCFinalizeMCReduceMemory: finalization of incremental full GC with
+  // memory reduction
+  HistogramTimer* GCTypeTimer(GarbageCollector collector);
+
   // ===========================================================================
   // Actual GC. ================================================================
   // ===========================================================================