Refactor http.Client and http.BaseClient to allow http.Client in type annotations.

pkg/http/lib/src/io_client.dart

 // Copyright (c) 2012, 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 client;
+library io_client;
 
 import 'dart:io';
 
 import 'base_client.dart';
 import 'base_request.dart';
 import 'streamed_response.dart';
 import 'utils.dart';
 
-/// An HTTP client which takes care of maintaining persistent connections across
-/// multiple requests to the same server. If you only need to send a single
-/// request, it's usually easier to use [head], [get], [post],
-/// [put], or [delete] instead.
-///
-/// When creating an HTTP client class with additional functionality, it's
-/// recommended that you subclass [BaseClient] and wrap another instance of
-/// [BaseClient] rather than subclassing [Client] directly. This allows all
-/// subclasses of [BaseClient] to be mutually composable.
-class Client extends BaseClient {
+/// A `dart:io`-based HTTP client. This is the default client.
+class IOClient extends BaseClient {
   /// The underlying `dart:io` HTTP client.
   HttpClient _inner;
 
   /// Creates a new HTTP client.
-  Client() : _inner = new HttpClient();
+  IOClient() : _inner = new HttpClient();
 
   /// Sends an HTTP request and asynchronously returns the response.
   Future<StreamedResponse> send(BaseRequest request) {
     var stream = request.finalize();
 
     var completer = new Completer<StreamedResponse>();
     var connection = _inner.openUrl(request.method, request.url);
     connection.onError = (e) {
       async.then((_) {
         // TODO(nweiz): remove this when issue 4974 is fixed
@@ skipping 34 matching lines @@
     return completer.future;
   }
 
   /// Closes the client. This terminates all active connections. If a client
   /// remains unclosed, the Dart process may not terminate.
   void close() {
     if (_inner != null) _inner.shutdown();
     _inner = null;
   }
 }