V8 support for cached accessors.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index 655da2ab2b97a53a9d2c077a68083b62d69ef931..cfc7297d63c083753ba85441160016bde06e6170 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -4637,6 +4637,8 @@ class V8_EXPORT Template : public Data {
    */
   void Set(Local<Name> name, Local<Data> value,
            PropertyAttribute attributes = None);
+  void SetPrivate(Local<Private> name, Local<Data> value,
+                  PropertyAttribute attributes = None);
   V8_INLINE void Set(Isolate* isolate, const char* name, Local<Data> value);
 
   void SetAccessorProperty(
@@ -5109,6 +5111,14 @@ class V8_EXPORT FunctionTemplate : public Template {
       Local<Value> data = Local<Value>(),
       Local<Signature> signature = Local<Signature>(), int length = 0);
 
+  /**
+   * Creates a function template backed/cached by a private property.
+   */
+  static Local<FunctionTemplate> NewWithCache(
+      Isolate* isolate, FunctionCallback callback,
+      Local<Private> cache_property, Local<Value> data = Local<Value>(),
+      Local<Signature> signature = Local<Signature>(), int length = 0);
+
   /** Returns the unique function instance in the current execution context.*/
   V8_DEPRECATE_SOON("Use maybe version", Local<Function> GetFunction());
   V8_WARN_UNUSED_RESULT MaybeLocal<Function> GetFunction(