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

src/global-handles.h

 // Copyright 2011 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.
 
 #ifndef V8_GLOBAL_HANDLES_H_
 #define V8_GLOBAL_HANDLES_H_
 
 #include "include/v8.h"
 #include "include/v8-profiler.h"
 
@@ skipping 163 matching lines @@
   static bool IsIndependent(Object** location);
 
   // Tells whether global handle is near death.
   static bool IsNearDeath(Object** location);
 
   // Tells whether global handle is weak.
   static bool IsWeak(Object** location);
 
   // Process pending weak handles.
   // Returns the number of freed nodes.
-  int PostGarbageCollectionProcessing(GarbageCollector collector);
+  int PostGarbageCollectionProcessing(
+      GarbageCollector collector, const v8::GCCallbackFlags gc_callback_flags);
 
   // Iterates over all strong handles.
   void IterateStrongRoots(ObjectVisitor* v);
 
   // Iterates over all handles.
   void IterateAllRoots(ObjectVisitor* v);
 
   // Iterates over all handles that have embedder-assigned class ID.
   void IterateAllRootsWithClassIds(ObjectVisitor* v);
 
@@ skipping 85 matching lines @@
 
   // Migrates data from the internal representation (object_group_connections_,
   // retainer_infos_ and implicit_ref_connections_) to the public and more
   // efficient representation (object_groups_ and implicit_ref_groups_).
   void ComputeObjectGroupsAndImplicitReferences();
 
   // v8::internal::List is inefficient even for small number of elements, if we
   // don't assign any initial capacity.
   static const int kObjectGroupConnectionsCapacity = 20;
 
+  class PendingPhantomCallback;
+
   // Helpers for PostGarbageCollectionProcessing.
+  static void InvokeSecondPassPhantomCallbacks(
+      List<PendingPhantomCallback>* callbacks, Isolate* isolate);
   int PostScavengeProcessing(int initial_post_gc_processing_count);
   int PostMarkSweepProcessing(int initial_post_gc_processing_count);
-  int DispatchPendingPhantomCallbacks();
+  int DispatchPendingPhantomCallbacks(bool synchronous_second_pass);
   void UpdateListOfNewSpaceNodes();
 
   // Internal node structures.
   class Node;
   class NodeBlock;
   class NodeIterator;
-  class PendingPhantomCallback;
+  class PendingPhantomCallbacksSecondPassTask;
 
   Isolate* isolate_;
 
   // Field always containing the number of handles to global objects.
   int number_of_global_handles_;
 
   // List of all allocated node blocks.
   NodeBlock* first_block_;
 
   // List of node blocks with used nodes.
@@ skipping 118 matching lines @@
   List<int> new_space_indices_;
   int singleton_handles_[NUMBER_OF_SINGLETON_HANDLES];
 
   DISALLOW_COPY_AND_ASSIGN(EternalHandles);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_GLOBAL_HANDLES_H_