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

src/api.cc

 // Copyright 2012 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 6011 matching lines @@
   i::HeapProfiler::DeleteAllSnapshots();
 }
 
 
 void HeapProfiler::DefineWrapperClass(uint16_t class_id,
                                       WrapperInfoCallback callback) {
   i::Isolate::Current()->heap_profiler()->DefineWrapperClass(class_id,
                                                              callback);
 }
 
+void HeapProfiler::VisitExternalResources(
+    v8::HeapProfiler::ExternalResourceVisitor* visitor) {
+  i::Isolate* isolate = i::Isolate::Current();
+  IsDeadCheck(isolate, "v8::HeapProfiler::VisitExternalResources");
 
+  class VisitorImpl : public i::HeapProfiler::ExternalResourceVisitor {
+   public:
+    VisitorImpl(v8::HeapProfiler::ExternalResourceVisitor* visitor)
+        : visitor_(visitor) {}
+    virtual ~VisitorImpl() {}
+    virtual void VisitExternalString(i::String* string) {
+      visitor_->VisitExternalString(Utils::ToLocal(
+          i::Handle<i::String>(string)));
+    }
+   private:
+    v8::HeapProfiler::ExternalResourceVisitor* visitor_;
+  } internal_visitor(visitor);
+  i::HeapProfiler::VisitExternalResources(&internal_visitor);
+}
 
 v8::Testing::StressType internal::Testing::stress_type_ =
     v8::Testing::kStressTypeOpt;
 
 
 void Testing::SetStressRunType(Testing::StressType type) {
   internal::Testing::set_stress_type(type);
 }
 
 int Testing::GetStressRuns() {
@@ skipping 115 matching lines @@
 
 
 char* HandleScopeImplementer::Iterate(ObjectVisitor* v, char* storage) {
   HandleScopeImplementer* scope_implementer =
       reinterpret_cast<HandleScopeImplementer*>(storage);
   scope_implementer->IterateThis(v);
   return storage + ArchiveSpacePerThread();
 }
 
 } }  // namespace v8::internal