[heap] Introduce enum of garbage collection reasons.

src/heap/scavenge-job.cc

 // Copyright 2015 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.
 
 #include "src/heap/scavenge-job.h"
 
 #include "src/base/platform/time.h"
 #include "src/heap/heap-inl.h"
 #include "src/heap/heap.h"
 #include "src/isolate.h"
@@ skipping 16 matching lines @@
       heap->tracer()->ScavengeSpeedInBytesPerMillisecond();
   size_t new_space_size = heap->new_space()->Size();
   size_t new_space_capacity = heap->new_space()->Capacity();
 
   job_->NotifyIdleTask();
 
   if (ReachedIdleAllocationLimit(scavenge_speed_in_bytes_per_ms, new_space_size,
                                  new_space_capacity)) {
     if (EnoughIdleTimeForScavenge(
             idle_time_in_ms, scavenge_speed_in_bytes_per_ms, new_space_size)) {
-      heap->CollectGarbage(NEW_SPACE, "idle task: scavenge");
+      heap->CollectGarbage(NEW_SPACE, GarbageCollectionReason::kIdleTask);
     } else {
       // Immediately request another idle task that can get larger idle time.
       job_->RescheduleIdleTask(heap);
     }
   }
 }
 
 bool ScavengeJob::ReachedIdleAllocationLimit(
     double scavenge_speed_in_bytes_per_ms, size_t new_space_size,
     size_t new_space_capacity) {
@@ skipping 55 matching lines @@
     v8::Isolate* isolate = reinterpret_cast<v8::Isolate*>(heap->isolate());
     if (V8::GetCurrentPlatform()->IdleTasksEnabled(isolate)) {
       idle_task_pending_ = true;
       auto task = new IdleTask(heap->isolate(), this);
       V8::GetCurrentPlatform()->CallIdleOnForegroundThread(isolate, task);
     }
   }
 }
 }  // namespace internal
 }  // namespace v8