[proxies] Implement Proxy.revocable.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index d139f326ec209015bf5098eaf068c9202f811892..cbf43c4e1141910cf9c033d9f7b9d27f5429a770 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -9500,7 +9500,7 @@ class JSProxy: public JSReceiver {
   // [handler]: The handler property.
   DECL_ACCESSORS(handler, Object)
   // [target]: The target property.
-  DECL_ACCESSORS(target, Object)
+  DECL_ACCESSORS(target, JSReceiver)
   // [hash]: The hash code property (undefined if not initialized yet).
   DECL_ACCESSORS(hash, Object)
 
@@ -9508,7 +9508,8 @@ class JSProxy: public JSReceiver {
 
   DECLARE_CAST(JSProxy)
 
-  bool IsRevoked() const;
+  INLINE(bool IsRevoked() const);
+  static Handle<Object> Revoke(Handle<JSProxy> proxy);
 
   // ES6 9.5.1
   static MaybeHandle<Object> GetPrototype(Handle<JSProxy> receiver);