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

sdk/lib/convert/html_escape.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:convert";
+part of dart.convert;
 
 /**
  * A `String` converter that converts characters to HTML entities.
  *
  * This is intended to sanitize text before inserting the text into an HTML
  * document. Characters that are meaningful in HTML are converted to
  * HTML entities (like `&` for `&`).
  *
  * The general converter escapes all characters that are meaningful in HTML
  * attributes or normal element context. Elements with special content types
@@ skipping 218 matching lines @@
     } else {
       _sink.add(val);
       if (isLast) _sink.close();
     }
   }
 
   void close() {
     _sink.close();
   }
 }