Provide a way for iterating through all external strings referenced from the JS heap

src/heap.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1336 matching lines @@
                         Context::NEXT_CONTEXT_LINK,
                         Heap::undefined_value(),
                         UPDATE_WRITE_BARRIER);
   }
 
   // Update the head of the list of contexts.
   global_contexts_list_ = head;
 }
 
 
+void Heap::VisitExternalResources(v8::ExternalResourceVisitor* visitor) {
+  CollectAllGarbage(kMakeHeapIterableMask);
+  AssertNoAllocation no_allocation;
+  HeapIterator iterator;
+  for (HeapObject* obj = iterator.next(); obj != NULL; obj = iterator.next()) {
+    if (obj->IsExternalString()) {
+      visitor->VisitExternalString(Utils::ToLocal(
+          i::Handle<i::String>(String::cast(obj))));
+    }
+  }
+}
+
+
 class NewSpaceScavenger : public StaticNewSpaceVisitor<NewSpaceScavenger> {
  public:
   static inline void VisitPointer(Heap* heap, Object** p) {
     Object* object = *p;
     if (!heap->InNewSpace(object)) return;
     Heap::ScavengeObject(reinterpret_cast<HeapObject**>(p),
                          reinterpret_cast<HeapObject*>(object));
   }
 };
 
@@ skipping 5265 matching lines @@
   isolate_->heap()->store_buffer()->Compact();
   isolate_->heap()->store_buffer()->Filter(MemoryChunk::ABOUT_TO_BE_FREED);
   for (chunk = chunks_queued_for_free_; chunk != NULL; chunk = next) {
     next = chunk->next_chunk();
     isolate_->memory_allocator()->Free(chunk);
   }
   chunks_queued_for_free_ = NULL;
 }
 
 } }  // namespace v8::internal