[JSON] implement indentation in the BasicJsonStringifier and expose via API.

test/mjsunit/json2.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 17 matching lines @@
 // Flags: --allow-natives-syntax --expose-externalize-string
 
 // Test JSON.stringify on the global object.
 var a = 12345;
 assertTrue(JSON.stringify(this).indexOf('"a":12345') > 0);
 assertTrue(JSON.stringify(this, null, 0).indexOf('"a":12345') > 0);
 
 // Test JSON.stringify of array in dictionary mode.
 function TestStringify(expected, input) {
   assertEquals(expected, JSON.stringify(input));
-  assertEquals(expected, JSON.stringify(input, null, 0));
+  assertEquals(expected, JSON.stringify(input, (key, value) => value));
+  assertEquals(JSON.stringify(input, null, "="),
+               JSON.stringify(input, (key, value) => value, "="));
 }
 
 var array_1 = [];
 var array_2 = [];
 array_1[1<<17] = 1;
 array_2[1<<17] = function() { return 1; };
 var nulls = "null,";
 for (var i = 0; i < 17; i++) {
   nulls += nulls;
 }
@@ skipping 20 matching lines @@
 // Note that toString function is not evaluated here!
 TestStringify('false', bool_wrapper);
 
 // Test getters.
 var counter = 0;
 var getter_obj = { get getter() {
                          counter++;
                          return 123;
                        } };
 TestStringify('{"getter":123}', getter_obj);
-assertEquals(2, counter);
+assertEquals(4, counter);
 
 // Test toJSON function.
 var tojson_obj = { toJSON: function() {
                              counter++;
                              return [1, 2];
                            },
                    a: 1};
 TestStringify('[1,2]', tojson_obj);
-assertEquals(4, counter);
+assertEquals(8, counter);
 
 // Test that we don't recursively look for the toJSON function.
 var tojson_proto_obj = { a: 'fail' };
 tojson_proto_obj.__proto__ = { toJSON: function() {
                                          counter++;
                                          return tojson_obj;
                                        } };
 TestStringify('{"a":1}', tojson_proto_obj);
 
 // Test toJSON produced by a getter.
@@ skipping 82 matching lines @@
 var str = "external";
 try {
   externalizeString(str, true);
 } catch (e) { }
 TestStringify("\"external\"", str, null, 0);
 
 var o = {};
 o.somespecialproperty = 10;
 o["\x19"] = 10;
 assertThrows("JSON.parse('{\"somespecialproperty\":100, \"\x19\":10}')");