Roll Observatory deps (charted -> ^0.3.0)

packages/usage/lib/src/usage_impl_io.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library usage_impl_io;
 
 import 'dart:async';
 import 'dart:convert' show JSON;
 import 'dart:io';
 
@@ skipping 21 matching lines @@
   if (index != -1) ver = ver.substring(0, index);
   return ver;
 }
 
 class IOPostHandler extends PostHandler {
   final String _userAgent;
   final HttpClient mockClient;
 
   IOPostHandler({HttpClient this.mockClient}) : _userAgent = _createUserAgent();
 
-  Future sendPost(String url, Map<String, String> parameters) {
+  Future sendPost(String url, Map<String, dynamic> parameters) {
     // Add custom parameters for OS and the Dart version.
     parameters['cd1'] = Platform.operatingSystem;
     parameters['cd2'] = 'dart ${_dartVersion()}';
 
     String data = postEncode(parameters);
 
     HttpClient client = mockClient != null ? mockClient : new HttpClient();
     client.userAgent = _userAgent;
     return client.postUrl(Uri.parse(url)).then((HttpClientRequest req) {
       req.write(data);
@@ skipping 25 matching lines @@
   void operator[]=(String key, dynamic value) {
     if (value == null) {
       _map.remove(key);
     } else {
       _map[key] = value;
     }
 
     _file.writeAsStringSync(JSON.encode(_map) + '\n');
   }
 }