Add data-URI support class to dart:core (next to Uri).

sdk/lib/convert/base64.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.convert;
 
 /**
  * An instance of [Base64Codec].
  *
  * This instance provides a convenient access to
@@ skipping 289 matching lines @@
   }
 }
 
 // ------------------------------------------------------------------------
 // Decoder
 // ------------------------------------------------------------------------
 
 class Base64Decoder extends Converter<String, List<int>> {
   const Base64Decoder();
 
-  List<int> convert(String input) {
-    if (input.isEmpty) return new Uint8List(0);
-    int length = input.length;
+  List<int> convert(String input, [int start = 0, int end]) {
+    end = RangeError.checkValidRange(start, end, input.length);
+    if (start == end) return new Uint8List(0);
     var decoder = new _Base64Decoder();
-    Uint8List buffer = decoder.decode(input, 0, input.length);
-    decoder.close(input, input.length);
+    Uint8List buffer = decoder.decode(input, start, end);
+    decoder.close(input, end);
     return buffer;
   }
 
   StringConversionSink startChunkedConversion(Sink<List<int>> sink) {
     return new _Base64DecoderSink(sink);
   }
 }
 
 /**
  * Helper class implementing base64 decoding with intermediate state.
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     end = RangeError.checkValidRange(start, end, string.length);
     if (start == end) return;
     Uint8List buffer = _decoder.decode(string, start, end);
     if (buffer != null) _sink.add(buffer);
     if (isLast) {
       _decoder.close(string, end);
       _sink.close();
     }
   }
 }