deps: V8: cherry-pick c721203

Original commit message:

    Add missing null condition in Proxy GetPrototypeof

    Bug: v8:9781
    Change-Id: I1f82a828f103cc2aa3f9553214f6b4867ffc3b17
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1829897
    Commit-Queue: Z Nguyen-Huu <duongn@microsoft.com>
    Reviewed-by: Georg Neis <neis@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#64049}

Refs: v8/v8@c721203
Fixes: nodejs#29730

common.gypi

@@ -39,7 +39,7 @@
 
     # Reset this number to 0 on major V8 upgrades.
     # Increment by one for each non-official patch applied to deps/v8.
-    'v8_embedder_string': '-node.14',
+    'v8_embedder_string': '-node.15',
 
     ##### V8 defaults for Node.js #####
 

deps/v8/src/builtins/proxy-get-prototype-of.tq

@@ -33,7 +33,7 @@ namespace proxy {
 
       // 8. If Type(handlerProto) is neither Object nor Null, throw a TypeError
       // exception.
-      if (!Is<JSReceiver>(handlerProto)) {
+      if (!Is<JSReceiver>(handlerProto) && handlerProto != Null) {
         goto ThrowProxyGetPrototypeOfInvalid;
       }
 

deps/v8/test/mjsunit/regress/regress-9781.js

@@ -0,0 +1,11 @@
+// Copyright 2019 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+var proto = Object.getPrototypeOf(new Proxy(Object.create(null), {
+  getPrototypeOf(target) {
+    return Reflect.getPrototypeOf(target);
+  }
+} ));
+
+assertEquals(proto, null);