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

sdk/lib/io/security_context.dart

 // Copyright (c) 2015, 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;
 
 /**
  * The object containing the certificates to trust when making
  * a secure client connection, and the certificate chain and
  * private key to serve from a secure server.
  *
  * The [SecureSocket]  and [SecureServerSocket] classes take a SecurityContext
  * as an argument to their connect and bind methods.
  *
  * Certificates and keys can be added to a SecurityContext from either PEM
@@ skipping 242 matching lines @@
     }
 
     if (bytes.length >= (1 << 13)) {
       throw new ArgumentError(
           'The maximum message length supported is 2^13-1.');
     }
 
     return new Uint8List.fromList(bytes);
   }
 }