Use patching for dart:io.

lib/io/string_stream.dart

Index: lib/io/string_stream.dart
diff --git a/runtime/bin/string_stream.dart b/lib/io/string_stream.dart
similarity index 99%
rename from runtime/bin/string_stream.dart
rename to lib/io/string_stream.dart
index 9cb9e29bc84c79735592192ad98c8fb513b42f54..63b4830f3897c794d62573709129d3ac9fdd9aca 100644
--- a/runtime/bin/string_stream.dart
+++ b/lib/io/string_stream.dart
@@ -61,7 +61,7 @@ class DecoderException implements Exception {
 
 // Utility class for decoding UTF-8 from data delivered as a stream of
 // bytes.
-class _StringDecoderBase implements _StringDecoder {
+abstract class _StringDecoderBase implements _StringDecoder {
   _StringDecoderBase()
       : _bufferList = new _BufferList(),
         _result = new List<int>(),
@@ -154,7 +154,7 @@ class _StringDecoderBase implements _StringDecoder {
     _resultOffset = 0;
   }
 
-  abstract bool _processNext();
+  bool _processNext();
 
   _BufferList _bufferList;
   int _resultOffset = 0;