Rewrite Error.prototype.toString in C++.

src/messages.h

Index: src/messages.h
diff --git a/src/messages.h b/src/messages.h
index 529c659e181d8f35cca3e05909d8e3a76fa9a3b4..d00eec0fc2131c5740f40103b0ac6a4bc864dcf4 100644
--- a/src/messages.h
+++ b/src/messages.h
@@ -457,6 +457,46 @@ class MessageHandler {
   static base::SmartArrayPointer<char> GetLocalizedMessage(Isolate* isolate,
                                                            Handle<Object> data);
 };
+
+
+class ErrorToStringHelper {
+ public:
+  ErrorToStringHelper() : visited_(0) {}
+
+  MUST_USE_RESULT MaybeHandle<String> Stringify(Isolate* isolate,
+                                                Handle<JSObject> error);
+
+ private:
+  class VisitedScope {
+   public:
+    VisitedScope(ErrorToStringHelper* helper, Handle<JSObject> error)
+        : helper_(helper), has_visited_(false) {
+      for (const Handle<JSObject>& visited : helper->visited_) {
+        if (visited.is_identical_to(error)) {
+          has_visited_ = true;
+          break;
+        }
+      }
+      helper->visited_.Add(error);
+    }
+    ~VisitedScope() { helper_->visited_.RemoveLast(); }
+    bool has_visited() { return has_visited_; }
+
+   private:
+    ErrorToStringHelper* helper_;
+    bool has_visited_;
+  };
+
+  static bool ShadowsInternalError(Isolate* isolate,
+                                   LookupIterator* property_lookup,
+                                   LookupIterator* internal_error_lookup);
+
+  static MUST_USE_RESULT MaybeHandle<String> GetStringifiedProperty(
+      Isolate* isolate, LookupIterator* property_lookup,
+      Handle<String> default_value);
+
+  List<Handle<JSObject> > visited_;
+};
 } }  // namespace v8::internal
 
 #endif  // V8_MESSAGES_H_