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

test/mjsunit/harmony/simd.js

 // Copyright 2015 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.
 
 // Flags: --harmony-simd
 // Flags: --allow-natives-syntax --expose-natives-as natives --noalways-opt
 
 function lanesForType(typeName) {
   // The lane count follows the first 'x' in the type name, which begins with
   // 'float', 'int', or 'bool'.
@@ skipping 604 matching lines @@
   assertSame(SIMD.foo, "foo");
   delete SIMD.foo;
   delete SIMD.Bool8x16;
   assertSame(SIMD.Bool8x16, undefined);
 }
 TestSIMDObject()
 
 
 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, "="));
 }
 
 TestStringify(undefined, SIMD.Float32x4(1, 2, 3, 4));
 TestStringify('[null]', [SIMD.Float32x4(1, 2, 3, 4)]);
 TestStringify('[{}]', [Object(SIMD.Float32x4(1, 2, 3, 4))]);
 var simd_wrapper = Object(SIMD.Float32x4(1, 2, 3, 4));
 TestStringify('{}', simd_wrapper);
 simd_wrapper.a = 1;
 TestStringify('{"a":1}', simd_wrapper);