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

test/mjsunit/harmony/simd.js

Index: test/mjsunit/harmony/simd.js
diff --git a/test/mjsunit/harmony/simd.js b/test/mjsunit/harmony/simd.js
index 1868050e50f5983226b16d546e791f0e7c08ab9d..a3d46159c1173eb3b03323de510b35dfc3caf722 100644
--- a/test/mjsunit/harmony/simd.js
+++ b/test/mjsunit/harmony/simd.js
@@ -622,7 +622,9 @@ 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));