[heap] Memory reducer calls GC with kGCCallbackFlagCollectAllExternalMemory flag.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index c43d3219c82800c6fdbb59bf6b4c5ac6c776bbee..264671c7eb0e3a86414fd0adf44d9171661c1708 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1239,7 +1239,9 @@ class Heap {
 
   // Start incremental marking and ensure that idle time handler can perform
   // incremental steps.
-  void StartIdleIncrementalMarking(GarbageCollectionReason gc_reason);
+  void StartIdleIncrementalMarking(
+      GarbageCollectionReason gc_reason,
+      GCCallbackFlags gc_callback_flags = GCCallbackFlags::kNoGCCallbackFlags);
 
   // Starts incremental marking assuming incremental marking is currently
   // stopped.