[heap] Introduce enum of garbage collection reasons.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index b500ef41fb16036a63982b6c0f46c25f19f861ab..343c7ad5a522985b6b4abbae505e07b391d8f8d7 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -512,7 +512,8 @@ StartupData SnapshotCreator::CreateBlob(
 
   // If we don't do this then we end up with a stray root pointing at the
   // context even after we have disposed of the context.
-  isolate->heap()->CollectAllAvailableGarbage("mksnapshot");
+  isolate->heap()->CollectAllAvailableGarbage(
+      i::GarbageCollectionReason::kSnapshotCreator);
   isolate->heap()->CompactWeakFixedArrays();
 
   i::DisallowHeapAllocation no_gc_from_here_on;
@@ -7477,8 +7478,7 @@ Local<Integer> v8::Integer::NewFromUnsigned(Isolate* isolate, uint32_t value) {
 void Isolate::ReportExternalAllocationLimitReached() {
   i::Heap* heap = reinterpret_cast<i::Isolate*>(this)->heap();
   if (heap->gc_state() != i::Heap::NOT_IN_GC) return;
-  heap->ReportExternalMemoryPressure(
-      "external memory allocation limit reached.");
+  heap->ReportExternalMemoryPressure();
 }
 
 
@@ -7638,13 +7638,13 @@ void Isolate::RequestGarbageCollectionForTesting(GarbageCollectionType type) {
   CHECK(i::FLAG_expose_gc);
   if (type == kMinorGarbageCollection) {
     reinterpret_cast<i::Isolate*>(this)->heap()->CollectGarbage(
-        i::NEW_SPACE, "Isolate::RequestGarbageCollection",
+        i::NEW_SPACE, i::GarbageCollectionReason::kTesting,
         kGCCallbackFlagForced);
   } else {
     DCHECK_EQ(kFullGarbageCollection, type);
     reinterpret_cast<i::Isolate*>(this)->heap()->CollectAllGarbage(
         i::Heap::kAbortIncrementalMarkingMask,
-        "Isolate::RequestGarbageCollection", kGCCallbackFlagForced);
+        i::GarbageCollectionReason::kTesting, kGCCallbackFlagForced);
   }
 }
 
@@ -8073,7 +8073,8 @@ void Isolate::LowMemoryNotification() {
     i::HistogramTimerScope idle_notification_scope(
         isolate->counters()->gc_low_memory_notification());
     TRACE_EVENT0("v8", "V8.GCLowMemoryNotification");
-    isolate->heap()->CollectAllAvailableGarbage("low memory notification");
+    isolate->heap()->CollectAllAvailableGarbage(
+        i::GarbageCollectionReason::kLowMemoryNotification);
   }
 }