Remove usage of dart:json.

utils/apidoc/mdn/postProcess.dart

 /**
  * Read database.json,
  * write database.filtered.json (with "best" entries)
  * and obsolete.json (with entries marked obsolete).
  */
 
 library postProcess;
 
+import 'dart:convert';
 import 'dart:io';
-import 'dart:json' as json;
 import 'util.dart';
 
 void main() {
   // Database of code documentation.
-  Map<String, List> database = json.parse(
+  Map<String, List> database = JSON.decode(
       new File('output/database.json').readAsStringSync());
   final filteredDb = {};
   final obsolete = [];
   for (String type in database.keys) {
     final entry = pickBestEntry(database[type], type);
     if (entry == null) {
       print("Can't find ${type} in database.  Skipping.");
       continue;
     }
     filteredDb[type] = entry;
     if (entry.containsKey("members")) {
       Map members = getMembersMap(entry);
       for (String name in members.keys) {
         Map memberData = members[name];
         if (memberData['obsolete'] == true) {
           obsolete.add({'type': type, 'member' : name});
         }
       }
     }
   }
-  writeFileSync("output/database.filtered.json", json.stringify(filteredDb));
-  writeFileSync("output/obsolete.json", json.stringify(obsolete));
+  writeFileSync("output/database.filtered.json", JSON.encode(filteredDb));
+  writeFileSync("output/obsolete.json", JSON.encode(obsolete));
 }