Revert "Change some platform libraries to use `part of URI`."

sdk/lib/io/secure_socket.dart

 // Copyright (c) 2013, 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.
 
-part of "dart:io";
+part of dart.io;
 
 /**
  * A high-level class for communicating securely over a TCP socket, using
  * TLS and SSL. The [SecureSocket] exposes both a [Stream] and an
  * [IOSink] interface, making it ideal for using together with
  * other [Stream]s.
  */
 abstract class SecureSocket implements Socket {
   external factory SecureSocket._(RawSecureSocket rawSocket);
 
@@ skipping 1213 matching lines @@
 
 /**
  * An exception that happens in the handshake phase of establishing
  * a secure network connection, when looking up or verifying a
  * certificate.
  */
 class CertificateException extends TlsException {
   const CertificateException([String message = "", OSError osError = null])
       : super._("CertificateException", message, osError);
 }