Let the second pass phantom callbacks run in a separate task on the foreground thread.

src/heap/heap.cc

 // Copyright 2012 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/v8.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/base/bits.h"
 #include "src/base/once.h"
@@ skipping 1288 matching lines @@
     mark_compact_collector_.marking_deque()->Uninitialize();
     mark_compact_collector_.EnsureMarkingDequeIsCommitted(
         MarkCompactCollector::kMinMarkingDequeSize);
   }
 
   gc_post_processing_depth_++;
   {
     AllowHeapAllocation allow_allocation;
     GCTracer::Scope scope(tracer(), GCTracer::Scope::EXTERNAL);
     freed_global_handles =
-        isolate_->global_handles()->PostGarbageCollectionProcessing(collector);
+        isolate_->global_handles()->PostGarbageCollectionProcessing(
+            collector, gc_callback_flags);
   }
   gc_post_processing_depth_--;
 
   isolate_->eternal_handles()->PostGarbageCollectionProcessing(this);
 
   // Update relocatables.
   Relocatable::PostGarbageCollectionProcessing(isolate_);
 
   double gc_speed = tracer()->CombinedMarkCompactSpeedInBytesPerMillisecond();
   double mutator_speed = static_cast<double>(
@@ skipping 5566 matching lines @@
     *object_type = "CODE_TYPE";                                                \
     *object_sub_type = "CODE_AGE/" #name;                                      \
     return true;
     CODE_AGE_LIST_COMPLETE(COMPARE_AND_RETURN_NAME)
 #undef COMPARE_AND_RETURN_NAME
   }
   return false;
 }
 }  // namespace internal
 }  // namespace v8