[heap] Introduce enum of garbage collection reasons.

src/heap/memory-reducer.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/memory-reducer.h"
 
 #include "src/flags.h"
 #include "src/heap/gc-tracer.h"
 #include "src/heap/heap-inl.h"
 #include "src/utils.h"
@@ skipping 55 matching lines @@
   DCHECK_EQ(kTimer, event.type);
   DCHECK_EQ(kWait, state_.action);
   state_ = Step(state_, event);
   if (state_.action == kRun) {
     DCHECK(heap()->incremental_marking()->IsStopped());
     DCHECK(FLAG_incremental_marking);
     if (FLAG_trace_gc_verbose) {
       PrintIsolate(heap()->isolate(), "Memory reducer: started GC #%d\n",
                    state_.started_gcs);
     }
-    heap()->StartIdleIncrementalMarking();
+    heap()->StartIdleIncrementalMarking(
+        GarbageCollectionReason::kMemoryReducer);
   } else if (state_.action == kWait) {
     if (!heap()->incremental_marking()->IsStopped() &&
         heap()->ShouldOptimizeForMemoryUsage()) {
       // Make progress with pending incremental marking if memory usage has
       // higher priority than latency. This is important for background tabs
       // that do not send idle notifications.
       const int kIncrementalMarkingDelayMs = 500;
       double deadline = heap()->MonotonicallyIncreasingTimeInMs() +
                         kIncrementalMarkingDelayMs;
       heap()->incremental_marking()->AdvanceIncrementalMarking(
           deadline, IncrementalMarking::NO_GC_VIA_STACK_GUARD,
           IncrementalMarking::FORCE_COMPLETION);
       heap()->FinalizeIncrementalMarkingIfComplete(
-          "Memory reducer: finalize incremental marking");
+          GarbageCollectionReason::kFinalizeMarkingViaTask);
     }
     // Re-schedule the timer.
     ScheduleTimer(event.time_ms, state_.next_gc_start_ms - event.time_ms);
     if (FLAG_trace_gc_verbose) {
       PrintIsolate(heap()->isolate(), "Memory reducer: waiting for %.f ms\n",
                    state_.next_gc_start_ms - event.time_ms);
     }
   }
 }
 
@@ skipping 100 matching lines @@
   auto timer_task = new MemoryReducer::TimerTask(this);
   V8::GetCurrentPlatform()->CallDelayedOnForegroundThread(
       isolate, timer_task, (delay_ms + kSlackMs) / 1000.0);
 }
 
 
 void MemoryReducer::TearDown() { state_ = State(kDone, 0, 0, 0.0); }
 
 }  // namespace internal
 }  // namespace v8