[heap] Introduce enum of garbage collection reasons.

src/heap/incremental-marking-job.cc

Index: src/heap/incremental-marking-job.cc
diff --git a/src/heap/incremental-marking-job.cc b/src/heap/incremental-marking-job.cc
index 14c6cf6c3913bb3efa7d4d43925c8db7cc1e82ac..799a1e2a1aaf90bb66b53144effea9d16e5afeaa 100644
--- a/src/heap/incremental-marking-job.cc
+++ b/src/heap/incremental-marking-job.cc
@@ -84,7 +84,9 @@ IncrementalMarkingJob::IdleTask::Progress IncrementalMarkingJob::IdleTask::Step(
           deadline_in_ms, IncrementalMarking::NO_GC_VIA_STACK_GUARD,
           IncrementalMarking::DO_NOT_FORCE_COMPLETION);
   if (remaining_idle_time_in_ms > 0.0) {
-    heap->TryFinalizeIdleIncrementalMarking(remaining_idle_time_in_ms);
+    heap->TryFinalizeIdleIncrementalMarking(
+        remaining_idle_time_in_ms,
+        GarbageCollectionReason::kFinalizeMarkingViaTask);
   }
   return incremental_marking->IsStopped() ? kDone : kMoreWork;
 }
@@ -123,7 +125,7 @@ void IncrementalMarkingJob::DelayedTask::Step(Heap* heap) {
       deadline, IncrementalMarking::NO_GC_VIA_STACK_GUARD,
       IncrementalMarking::FORCE_COMPLETION);
   heap->FinalizeIncrementalMarkingIfComplete(
-      "Incremental marking task: finalize incremental marking");
+      GarbageCollectionReason::kFinalizeMarkingViaTask);
 }