[json] handle proxies in BasicJsonSerializer.

test/mjsunit/es6/proxies-json.js

 // 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 489 matching lines @@
 
 var result = JSON.parse('{"foo":0,"bar":1}', reviver);
 assertEquals({foo: 0, bar: proxy}, result);
 assertSame(result.bar, proxy);
 assertEquals(3, log.length);
 for (var i in log) assertSame(target, log[i][1]);
 
 assertEquals(["get", target, "length", proxy], log[0]);
 assertEquals(["get", target, "0", proxy], log[1]);
 assertEquals(["deleteProperty", target, "0"], log[2]);
+
+proxy = new Proxy([], {
+  get: function(target, property) {
+    if (property == "length") return 7;
+    return 0;
+  },
+});
+assertEquals('[[0,0,0,0,0,0,0]]', JSON.stringify([proxy]));
+
+proxy = new Proxy([], {
+  get: function(target, property) {
+    if (property == "length") return 1E40;
+    return 0;
+  },
+});
+assertThrows(() => JSON.stringify([proxy]), RangeError);
+
+log = [];
+proxy = new Proxy({}, {
+  ownKeys: function() {
+    log.push("ownKeys");
+    return ["0", "a", "b"];
+  },
+  get: function(target, property) {
+    log.push("get " + property);
+    return property.toUpperCase();
+  },
+  getOwnPropertyDescriptor: function(target, property) {
+    log.push("descriptor " + property);
+    return {enumerable: true, configurable: true};
+  },
+  isExtensible: assertUnreachable,
+  has: assertUnreachable,
+  getPrototypeOf: assertUnreachable,
+  setPrototypeOf: assertUnreachable,
+  preventExtensions: assertUnreachable,
+  setPrototypeOf: assertUnreachable,
+  defineProperty: assertUnreachable,
+  set: assertUnreachable,
+  deleteProperty: assertUnreachable,
+  apply: assertUnreachable,
+  construct: assertUnreachable,
+});
+
+assertEquals('[{"0":"0","a":"A","b":"B"}]', JSON.stringify([proxy]));
+assertEquals(['get toJSON',
+              'ownKeys',
+              'descriptor 0',
+              'descriptor a',
+              'descriptor b',
+              'get 0',
+              'get a',
+              'get b'], log);