Re-apply "Add a non-dart:io WebSocket implementation to http_parser."

pkg/http_parser/lib/src/bytes_builder.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;
+// This is a copy of "dart:io"'s BytesBuilder implementation, from
+// sdk/lib/io/bytes_builder.dart. It's copied here to make it available to
+// non-"dart:io" applications (issue 18348).
+//
+// Because it's copied directly, there are no modifications from the original.
+library http_parser.bytes_builder;
+
+import 'dart:math';
+import 'dart:typed_data';
 
 /**
  * Builds a list of bytes, allowing bytes and lists of bytes to be added at the
  * end.
  *
  * Used to efficiently collect bytes and lists of bytes.
  */
 abstract class BytesBuilder {
   /**
    * Construct a new empty [BytesBuilder].
@@ skipping 181 matching lines @@
 
   bool get isEmpty => _length == 0;
 
   bool get isNotEmpty => _length != 0;
 
   void clear() {
     _length = 0;
     _chunks.clear();
   }
 }