[heap] Introduce enum of garbage collection reasons.

src/runtime/runtime-debug.cc

Index: src/runtime/runtime-debug.cc
diff --git a/src/runtime/runtime-debug.cc b/src/runtime/runtime-debug.cc
index 0ac448846c92f0ccc0fa2da3e40ccd483d9e8c5a..2d217b83f7fc8d3ddd0b60f7355794994aeb09e8 100644
--- a/src/runtime/runtime-debug.cc
+++ b/src/runtime/runtime-debug.cc
@@ -1522,7 +1522,8 @@ RUNTIME_FUNCTION(Runtime_GetDebugContext) {
 RUNTIME_FUNCTION(Runtime_CollectGarbage) {
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 1);
-  isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags, "%CollectGarbage");
+  isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
+                                     GarbageCollectionReason::kRuntime);
   return isolate->heap()->undefined_value();
 }