Don't crash when decoding astral plane UTF-8.

sdk/lib/io/string_stream.dart

 // Copyright (c) 2012, 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.
 
 // Interface for decoders decoding binary data into string data. The
 // decoder keeps track of line breaks during decoding.
 abstract class _StringDecoder {
   // Add more binary data to be decoded. The ownership of the buffer
   // is transfered to the decoder and the caller most not modify it any more.
   int write(List<int> buffer);
@@ skipping 67 matching lines @@
         break;
       }
     }
     return buffer.length;
   }
 
   bool get isEmpty => _result.isEmpty;
 
   int get lineBreaks => _lineBreaks;
 
-  String decoded([int len]) {
+  String decoded([int length]) {
     if (isEmpty) return null;
 
-    String result;
-    if (len !== null && len < available()) {
-      result = new String.fromCharCodes(_result.getRange(_resultOffset, len));
+    List<int> result;
+    if (length != null && length < available()) {
+      result = _result.getRange(_resultOffset, length);
+    } else if (_resultOffset == 0) {
+      result = _result;
     } else {
-      if (_resultOffset == 0) {
-        result = new String.fromCharCodes(_result);
-      } else {
-        result =
-            new String.fromCharCodes(
-                _result.getRange(_resultOffset,
-                                 _result.length - _resultOffset));
-      }
+      result = _result.getRange(_resultOffset, _result.length - _resultOffset);
     }
+
     _resultOffset += result.length;
     while (!_lineBreakEnds.isEmpty &&
            _lineBreakEnds.first < _charOffset + _resultOffset) {
       _lineBreakEnds.removeFirst();
       _lineBreaks--;
     }
     if (_result.length == _resultOffset) _resetResult();
-    return result;
+    return new String.fromCharCodes(result);
   }
 
   String get decodedLine {
     if (_lineBreakEnds.isEmpty) return null;
     int lineEnd = _lineBreakEnds.removeFirst();
     int terminationSequenceLength = 1;
     if (_result[lineEnd - _charOffset] == LF &&
         lineEnd > _charOffset &&
         _resultOffset < lineEnd &&
         _result[lineEnd - _charOffset - 1] == CR) {
@@ skipping 290 matching lines @@
     _checkInstallDataHandler();
     _checkScheduleCallback();
   }
 
   void set onClosed(void callback()) {
     _clientCloseHandler = callback;
   }
 
   void set onError(void callback(e)) {
     _input.onError = callback;
-    _decoder.onError = (e) { 
+    _decoder.onError = (e) {
       _clientCloseHandler = null;
       _input.close();
       callback(e);
     };
   }
 
   void _onData() {
     _readData();
     if (!_decoder.isEmpty && _clientDataHandler !== null) {
       _clientDataHandler();
@@ skipping 104 matching lines @@
   bool _inputClosed = false;  // Is the underlying input stream closed?
   bool _closed = false;  // Is this stream closed.
   bool _eof = false;  // Has all data been read from the decoder?
   Timer _scheduledDataCallback;
   Timer _scheduledLineCallback;
   Timer _scheduledCloseCallback;
   Function _clientDataHandler;
   Function _clientLineHandler;
   Function _clientCloseHandler;
 }