- Fix use of String operator + in runtime and standalone libraries.

runtime/bin/file_impl.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.
 
 class _FileInputStream extends _BaseDataInputStream implements InputStream {
   _FileInputStream(String name) {
     _file = new File(name);
     _data = [];
     _position = 0;
     _file.onError = (String s) {
@@ skipping 413 matching lines @@
     return new Directory(_FileUtils.directory(_name));
   }
 
   void open(FileMode mode, void callback(RandomAccessFile file)) {
     _ensureFileService();
     _asyncUsed = true;
     if (mode != FileMode.READ &&
         mode != FileMode.WRITE &&
         mode != FileMode.APPEND) {
       if (_onError != null) {
-        _onError("Unknown file mode. Use FileMode.READ, FileMode.WRITE " +
+        _onError("Unknown file mode. Use FileMode.READ, FileMode.WRITE "
                  "or FileMode.APPEND.");
         return;
       }
     }
     List request = new List(3);
     request[0] = _FileUtils.kOpenRequest;
     request[1] = _name;
     request[2] = mode._mode;  // Direct int value for serialization.
     _fileService.call(request).receive((id, replyTo) {
       if (id != 0) {
         callback(new _RandomAccessFile(id, _name));
       } else if (_onError != null) {
         _onError("Cannot open file: $_name");
       }
     });
   }
 
   RandomAccessFile openSync([FileMode mode = FileMode.READ]) {
     if (_asyncUsed) {
       throw new FileIOException(
           "Mixed use of synchronous and asynchronous API");
     }
     if (mode != FileMode.READ &&
         mode != FileMode.WRITE &&
         mode != FileMode.APPEND) {
-      throw new FileIOException("Unknown file mode. Use FileMode.READ, " +
+      throw new FileIOException("Unknown file mode. Use FileMode.READ, "
                                 "FileMode.WRITE or FileMode.APPEND.");
     }
     var id = _FileUtils.checkedOpen(_name, mode._mode);
     if (id == 0) {
       throw new FileIOException("Cannot open file: $_name");
     }
     return new _RandomAccessFile(id, _name);
   }
 
   static RandomAccessFile _openStdioSync(int fd) {
@@ skipping 572 matching lines @@
   bool _asyncUsed;
   int _pendingWrites = 0;
 
   SendPort _fileService;
 
   Timer _noPendingWriteTimer;
 
   Function _onNoPendingWrites;
   Function _onError;
 }