Reland "Merge more Kernel infrastructure from kernel_sdk SDK fork."

runtime/lib/uri_patch.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.
 
-import "dart:convert" show ASCII;
-
 // VM implementation of Uri.
 typedef Uri _UriBaseClosure();
 
 Uri _unsupportedUriBase() {
   throw new UnsupportedError("'Uri.base' is not supported");
 }
 
 // _uriBaseClosure can be overwritten by the embedder to supply a different
 // value for Uri.base.
 _UriBaseClosure _uriBaseClosure = _unsupportedUriBase;
@@ skipping 49 matching lines @@
       } else {
         const String hexDigits = '0123456789ABCDEF';
         result..writeCharCode(_PERCENT)
               ..writeCharCode(hexDigits.codeUnitAt(byte >> 4))
               ..writeCharCode(hexDigits.codeUnitAt(byte & 0x0f));
       }
     }
     return result.toString();
   }
 }