Add memory pressure notification API

src/heap/incremental-marking.h

Index: src/heap/incremental-marking.h
diff --git a/src/heap/incremental-marking.h b/src/heap/incremental-marking.h
index 8b4aa86efc04250ef98174506a558d2e524cb425..6e392ed2d299c26099e7864ae0dcd45e749d0a2f 100644
--- a/src/heap/incremental-marking.h
+++ b/src/heap/incremental-marking.h
@@ -29,7 +29,7 @@ class IncrementalMarking {
 
   enum ForceCompletionAction { FORCE_COMPLETION, DO_NOT_FORCE_COMPLETION };
 
-  enum GCRequestType { COMPLETE_MARKING, FINALIZATION };
+  enum GCRequestType { NONE, COMPLETE_MARKING, FINALIZATION };
 
   struct StepActions {
     StepActions(CompletionAction complete_action_,
@@ -80,6 +80,8 @@ class IncrementalMarking {
 
   GCRequestType request_type() const { return request_type_; }
 
+  void reset_request_type() { request_type_ = NONE; }
+
   bool CanBeActivated();
 
   bool ShouldActivateEvenWithoutIdleNotification();